My dad kind of stalks me so what I do is create a fake “bait” account that I do everything with that’s considered “acceptable.” Then I have a secret account he doesn’t have access to. If you have a connected Apple ID or shared history— get your own Apple ID or only visit your secret account on an Incognito account (the full history WILL show on the Wifi bill though I think). The bait account usually prevents from further snooping if it’s convincing enough.
Dang, there’s nothing you can do about the school account besides delete all the emails then… I would suggest a secret email for any hiding any stuff in the future. My teachers/counselors were understanding when I explained stuff to them and asked to speak w/ an outside email (but keep in mind they ARE mandatory reporters first).
That’s rough, my dad likes being financial controlling so I get it. The best you can do right now is create a long term plan to eventually remove yourself from the situation with the resources you have / will have in the future. I went to a college out of state to create physical distance, which helps. Whatever help or people who will support you leaving, don’t be afraid to lean on them (reasonably of course). Realistically, it takes a few years to get a good standing on your own. Good luck.