Both yes
In general Yes, but that might be different in the case of upgrades (jumps from one major android to the next or further:
Well, it’s a smartphone so do not exoect miracles, especially if you use it as a portable computer (which it is) for online services etc. like banking … That said: with a fairly good battery and only cell phone on and not too many apps that eat up battery in the background and with a not too bright display etc 2 full days should be doable.
Notifications would not worry me much - depending on how many to expect (see above: number of apps running in the background)
Depends: [LIST] Banking Apps on /e/OS