Yes, yes and yes. It kind of depends what your project uses under the hood and what it depends on, but Astro is quite flexible with the frameworks it supports and for many things there’s a first-class integration that lets you just install support for certain libraries and frameworks (for example Tailwind, React, Partytown, certain CMSes) with one command.

For DB and user logins, you might have to run in SSR mode to be able to do server-side stuff, but you can certainly build API routes, server middleware and interact with cookies for user token stuff.