Your site needs three concurrent efforts: restore stability & security, modernize user experience (mobile-first checkout), and implement reliable commerce plumbing (catalog, inventory, payments, fulfillment) — done in prioritized, testable steps so business continues during migration.

Root-problem checklist (what “outdated & not functional” usually means)

• Broken or inconsistent checkout flow (errors, missing payment options)

• Slow page load and poor mobile UX → high bounce/abandonment

• No or fragile inventory/order management → oversells or manual reconciliation

• Security holes (expired TLS, outdated platform/plugins)

• Poor SEO / canonicalization & broken links → lost organic traffic

• Hard-to-update CMS / monolithic design → costly feature changes

• No analytics or incomplete events → cannot measure conversion funnel

• Weak 3rd-party integrations (shipping, tax, ERP) or none at all

Goals & success metrics (what “fixed” looks like)

Primary business goals:

• Increase checkout completion rate

• Reduce cart abandonment

• Enable dependable multi-channel selling

• Reduce manual order handling / errors

KPIs to track (define baseline now):

• Conversion rate (sessions → purchases)

• Cart abandonment rate

• Page load time (LCP, TTFB)

• Checkout error rate (exceptions per 100 checkouts)

• Time-to-fulfill / shipping SLA compliance

• Uptime / incident frequency

• Average order value (AOV)

• Organic traffic & revenue

Acceptance criteria (example, measurable):

• Checkout successfully completes 99% of test transactions across supported payment methods.

• Mobile-first pages render LCP ≤ target (choose target per audience) and < X seconds TTFB.

• No “out of stock but sold” incidents in production for normal order volumes.

• TLS valid + no critical OWASP vulnerabilities from a scan.

Prioritized action plan (no timelines — just priority order)

A. Immediate — Quick wins (do these first, low cost / high impact)

1. Take a snapshot / backup of site & DB (full, offsite).
   Acceptance: backups verified (restore test on staging).

2. Fix critical security gaps: update TLS cert, patch core platform/plugins, rotate admin credentials, remove unused admin accounts.
   Acceptance: external scan shows no critical issues.

3. Enable or repair analytics & error logging (Google Analytics/GA4, server logs, Sentry) so you can measure problems.
   Acceptance: Checkout errors logged with context; GA records purchases and key funnel events.

4. Restore a working checkout flow (even if basic): allow at least one reliable payment method and one shipping method.
   Acceptance: Test purchases succeed and orders recorded in DB.

5. Clean up visible site bugs (broken images, missing product data, major JS errors).
   Acceptance: No JS console errors on core paths.

Why first: these reduce immediate revenue loss and let you measure problems.

B. Stabilize platform (foundation improvements)

1. Health & performance audit

   • Run automated performance audit (Lighthouse) and a security scan (OWASP + dependency checks).
     Deliverables: prioritized list of issues by business impact.

2. Fix hosting & caching

   • Use CDN for static content, enable server-side caching or Varnish, tune database connections, inspect hosting resources.
     Acceptance: consistent lower TTFB and fewer timeouts under expected load.

3. Mobile UX fixes (mobile-first checkout, big CTAs, simplified forms)

   • Reduce required fields, input masks, auto-fill, optimize keyboard on mobile, visible progress indicator in checkout.

4. Test coverage & QA flow

   • Add regression tests for key journeys (browse → add to cart → checkout). Use automated UI tests + manual test matrix.

5. Data integrity

   • Normalize product data (titles, SKUs, tax codes, categories), remove duplicate/obsolete SKUs, fix inventory logic.

Why: these reduce downtime, reduce friction, and prevent operational errors.

C. Build reliable e-commerce plumbing (features & processes)

1. Rebuild or harden catalog & inventory system

   • Single source of truth for SKUs, stock levels, variants, pricing rules, promotions.

   • Enforce transactional inventory updates to prevent oversells.

2. Payments: implement robust providers & fallback

   • Primary provider(s) for region (local wallets/gateways) + fallback (card gateway, manual bank transfer). Ensure tokenization and PCI compliance (or use hosted checkout).

   • Implement clear error messages and retry logic.

3. Checkout UX improvements

   • One-page checkout or progressive multi-step with validation & save-for-later.

   • Guest checkout + ability to create account after purchase.

4. Shipping & taxes integration

   • Integrate with shipping providers for rates & tracking. Automate tax calculation or set validated default tax rules.

5. Order management & fulfillment

   • Dashboard for staff to view, process, and update orders; notifications for exceptions.

6. Customer accounts & returns

   • Order history, invoice generation, return portal or RMA flow.

7. Testing payment & fraud

   • Monitor fraudulent patterns; set up risk checks and 3DS when needed.

Why: commerce must be accurate, auditable, and forgiving for users.

D. Growth & polish (after core reliability)

• Personalization & merchandising (recommendations, cross-sell)

• Email flows: abandoned cart recovery, post-purchase, re-engagement

• SEO improvements: structured data, canonicalization, sitemap, meta tags

• Performance edge cases: image optimization, critical CSS, modern image formats

• A/B testing for conversion optimization

• Internationalization / multi-currency (if relevant)

• Marketing integrations (ads, social, marketplaces)

Technical recommendations (stack & architecture options)

Pick what fits your team; below are robust, maintainable options.

• If you want a developer-first, scalable stack: Backend (Django + Django Oscar or Saleor), Frontend (React / Next.js or plain server-side rendered Django templates), PostgreSQL, Redis for caching & session, Celery for background jobs. Payment via gateway APIs (tokenized).

• If you prefer CMS + plugins: WordPress + WooCommerce — fast to launch, needs strict plugin hygiene & managed hosting.

• If enterprise: Magento or commercetools; heavier but feature-rich.

• Headless / API-first: Consider separating front-end (React/Vue) and backend commerce API for flexibility and faster UI iteration.

• Hosting: Managed cloud (AWS, DigitalOcean App Platform, Render, or PaaS) with autoscaling and CDN.

Choose platform based on: traffic volume, dev skills (you mentioned Django before), integration complexity, and budget.

UX & checkout specifics (convert more visitors)

Essential UX fixes:

• Prominent shipping/time & returns info on product pages.

• Trust signals: TLS badge, payment provider logos, reviews.

• Cart preview that persists across sessions.

• Clear progress steps in checkout + inline validation.

• Minimal fields; autopopulate address via postal code lookup if available.

• Show total costs early (include shipping & taxes) to avoid surprises.

• Multiple payment options (card, local e-wallets, cash-on-delivery if business supports).

Acceptance test example: run 50 real-device flows (iOS/Android, desktop) covering common countries/cards and ensure 100% complete with no JS errors and correct totals.

Operational/process recommendations

• Support & SLA: create playbook for outages; provide staff with manual order entry procedure if gateway is down.

• Inventory reconciliation: daily automatic sync + manual exception queue.

• Fraud & chargebacks: set fraud rules, identity checks, and reusable dispute process.

• Legal: T&Cs, privacy policy, cookie consent, refund policy, GDPR/local regulations compliance.

• Customer service: integrated helpdesk (Zendesk, Freshdesk) with order pull-ups.

Monitoring, QA & release controls

• Monitoring: Uptime monitor (Pingdom/Uptrends), application performance monitoring (New Relic / Datadog / Sentry).

• Logging: centralized logs (ELK, Datadog), structured logs with order IDs for fast tracing.

• CI/CD: automated tests run on PRs; promote to staging then production with feature flags.

• Rollback plan: maintain deployable previous version and DB migration rollbacks.

Testing matrix (must-have tests before launch)

• Functional: browse → add → checkout (all payment methods), returns, refunds, promotions, taxes.

• Load test: simulated concurrent users on checkout path and product pages.

• Security: dependency and vuln scans, penetration test on sensitive endpoints.

• Regression: major UI flows after any release.

SEO & content recovery (if traffic dropped)

• Fix broken URLs & 301 redirects for renamed pages.

• Generate XML sitemap and submit to search engines.

• Fix canonical tags to avoid duplicate content.

• Add structured data for products (price, availability) to improve SERP.

• Preserve URL structure during migration or map redirects.

Example acceptance checklist for “site is e-commerce ready”

• All product pages correct and show: price, stock, shipping estimate, add-to-cart.

• Checkout completes with audit trail for orders and payment confirmations.

• Inventory updates atomically and is accurate across channels.

• Payment processing logs show no unhandled errors during test transactions.

• Analytics captures funnel events (product_view, add_to_cart, begin_checkout, purchase).

• No critical security vulnerabilities found in recent scan.

Common pitfalls & how to mitigate

• Relying on many plugins (creates maintenance debt) → prefer core integrations or vetted microservices.

• Poor data quality (bad SKUs, missing images) → invest in data clean-up before marketing pushes.

• Cutting QA to save time → causes revenue loss. Maintain regression suite.

• Ignoring mobile-first → most traffic will be mobile; optimize it first.

Risks & contingency

• Payment provider downtime: have manual payment acceptance and clear messaging.

• Migration data loss: validate with staging restore tests.

• SEO traffic dip after migration: prepare full redirect map + monitor index coverage.

Practical next steps I recommend you ask your team/vendor to do now

1. Take full backups and create a staging environment (if none exists).

2. Run a performance & security audit and share the report.

3. Triage the audit into “critical” (blockers), “high” (conversion killers), and “nice-to-have”.

4. Implement immediate fixes from the “critical” bucket (checkout stability, TLS, analytics).

5. Start building automated tests for the checkout funnel.

If you want, I can:

• Produce a specific technical audit checklist tailored to your current platform (I’ll need the platform name and hosting details).

• Create the regression test matrix & sample test cases for QA.

• Draft a minimal “launch checklist” your ops team can use.