Upgrade PHP & DB Stack

I have an established web application that still runs on PHP 5.4 with a MySQL 5.6 backend. I now need it running smoothly on PHP 7.4 and PostgreSQL. A staging server is already in place so you can work safely without touching production.

The codebase relies on a few specific frameworks and libraries (I’ll give you the full list and versions once we start). Your job is to modernise the code, replace or shim deprecated functions, update third-party packages as required, and translate all MySQL queries—including schema definitions, stored routines, and raw SQL—into efficient PostgreSQL equivalents.

Acceptance criteria
• Application installs and runs on PHP 7.4 without warnings or deprecated notices.
• All existing features behave identically on PostgreSQL (schema and data migrated).
• Automated and manual tests pass on the staging server.
• Deployment notes explain required server settings and any library upgrades.

If you have solid experience migrating legacy PHP projects and handling MySQL-to-PostgreSQL data moves, I’d love to hear how you would tackle this and an estimated timeline.