A different launcher. There’s a ton of them.
If you need some inspiration … Android 7 Nougat / 8 Oreo / 9 Pie: Home screens / Launchers
With a different launcher you could remove the icons from the home screen.
If you really want to uninstall system Apps … First Steps after installing /e/OS | removing bloatware
The pre-installed Weather Widget seems connected to Bliss launcher.
I use a different launcher, and I don’t have this Widget anymore.
As for location … is the location in e.g. Magic Earth correct for you?
Unlocking (and locking) the bootloader will automatically wipe the data partition for security reasons.
Whether installing Magisk really requires this, I don’t know. (I saw this mentioned here somewhere, too, but I didn’t root, so I can’t say for sure.)
Since Fairphone and /e/ are official partners, I would expect Fairphone to hand over their firmware changes to /e/. But I don’t know how to verify that.
There is no modem.zip you can flash on the Fairphone 3.
You would have to ask the developers, but [ROM][UNOFFICIAL] LineageOS 16.0 for FP3 was started before /e/ was officially released for the Fairphone 3.