I didn't read the entire thread but I can give my feedback: I've been running /e/ on a Fairphone 3+ for more than 4 years now (October 2020) and it's been good so far. It works with all the Android apps I've tested, including 3 different banking apps. Especially since 1.0 came out it's been really good.
The only problem right now is they're having a big cloud outage and the file storing system has been down for 4 months. Still works for calendar, mail, tasks and contacts sync though, but I'm not sure I'd recommend creating an /e/ account right now. Since it's a Nextcloud integration you can create any Nextcloud account and sync it with /e/ so it's quite okay! Or just run the phone with no account since both work.
