1. Should I buy a Switch now, or wait for a deal on BF or closer to Christmas? I feel like Nintendo doesn’t often do major discounts or bundles. So would I get the same deal now as I would during BF/the holidays?
The Switch may not be discounted for awhile now, so you could be waiting awhile for that. I'd say go for the console if the library's big enough and appealing enough for you to warrant the purchase.
2. I realllly would like to play the old Super Mario Galaxy games. Can I buy these and other prior-gen Nintendo games digitally on the Switch/Nintendo store? Or is the Switch BC?
Sadly no, but that could change at some point in time.
3. Will I be able to enjoy Zelda BotW if I’ve never played a Zelda game before?
Definitely! Most of the games are standalone, so no need to know any backstory from older games.
4. Is there any peripheral or anything else I have to buy other than what comes with the Switch? I’ve heard people talk about some alternate controller? Not sure what that’s about...
It depends on you, but you may need a larger SD card for more storage space, and if you don't like the joy cons, you may want to get the pro controller. There's also the chance you'll need more controllers for MP games.
Sorry I know so little about Nintendo/the Switch. But thank you in advance for any and all answers! :) And any other tips or useful info you want to share is welcome as well!
If you worry about your screen getting scratches, perhaps consider getting a screen protector too.