Ironically, I bought a refurbished Google pixel last year just because it supported calyxos. Never looked back. Just recently they added support for more devices which is great.
If you don't run anything Google on your device, you'll discover that an oldish (~4 years old) phone is plenty.
Some app recommendations:
* mapping: osmand
* e-mail: k-9 mail
* app stores: f-droid + Aurora store
* contacts & calendar sync: davx
* camera: open camera
* YouTube: newpipe