My advice would be to look into things one at a time while also avoiding taking the sledgehammer approach. Based on what you mentioned, some things you might want to look into:

Look into some encrypted cloud storage/backup options. Filein comes to mind but there’s plenty. I’d recommend against self hosting your own cloud in most cases (like nextcloud) in most cases it is both less secure and less private especially on a VPS - and if its on a home server it makes your backups less redundant.

Try doing more stuff in web browsers, web wrappers, or front ends. Unlike an app, there’s a lot less sneaky stuff a web browser can do, even if it’s the same platform. The Brave browser does cookie isolation and progressive web apps well, it might make a good second browser dedicated to progressive web apps. Apps like newpipe are great for YouTube and piped/invidious for yt or nitter for twitter are two good examples of front ends.

Installing apks is easier than you might think, and if you install FDroid it’s three clicks (download, allow installation, install) and worth checking out. Once it’s installed you can treat it like any other app store, and in combo with Aurora (on FDroid) you can get about any app without going through a Google account.

As for email, you can forward emails from a gmail account to a proton account. And as for content, consider trying to follow via RSS (you can follow just about anything with RSS one way or another).

For social media look into activity pub and nostr. Just about any alternative social media is going to have the crazies from one or both sides of politics kicked off of mainstream platforms, but federated and decentralized platforms allow you to pick and choose a lot more.

Last, as the phone goes, whenever possible try disabling background data and setting aside pre-installed apps you don’t want to use and going from there. A step up from that would be to uninstall/disable them (either in settings or adb bridge for those you can’t disable). Custom Roms would be the biggest leap, and the most technological. If you’re going to buy a phone with the intent of installing one, Graphene beats everything else hands down while still being one of the easiest to install.

Good luck