As others have mentioned, you can setup email forwarding to a master inbox.
Alternatively, you can use an email client set up with multiple email accounts. I use IMClient on Windows for this.
For multiple login sessions, some browsers have this as a feature. I can't really remember which from the top of my head, but I think Vivaldi, Opera GX and Brave have this built-in. Otherwise, you can use the SessionBox browser extension
I began making the move to UnGoogled Chromium last night. So far so good. Figuring out how to live without containers though... that's tough. So far the free version of SessionBox seems to be okay and gives me some of what I need:
Solved it for Chrome using the stackoverflow link provided by gobstopped with Tampermonkey, quick & dirtier (It's the "@run-at document-start" bit that does it):
// ==UserScript==
// default metadata...
// @run-at document-start
// ==/UserScript==
window.webkitRequestFileSystem = 'fEck off, wachinton';
And that's it.
Though, reading about Firefox containers got me looking for a Chrome alternative and I stumbled upon this extension. It looks like it's worth a try!
Try the add-on from https://sessionbox.io/ instead of FF multi-containers, I've been using it for a while and am very happy with it.
To the op, IMO uBlock Origin together with Decentraleyes will render FF's built in protection useless.