High school isn't something to get worked up over. Trust me, it's not worth getting all dressed up all fancy over. But again that's my opinion, you make your own decisions. That's the beauty of growing up.
It's not too much (In my personal opinion), though I would wear some flats. You're going to be doing a LOT of running to your classes in the hallways. Also, I'm becoming a Junior, and as I went through high school people started caring less and less about what they wear on the first day lol
Yeah most people just wear jeans and a tee or a nice shirt and some jeans. It highschool don't worry too much everyone is too nervous and bored to care what your wearing. Also I definetly don't recommend heels for the first day.
I would stick with a nice pair of jeans and a cute top maybe with a kimono, or whatever is your style. Also if you live somewhere where it is quite chilly, I would defintley reccomend a nice pair of Chelsea boots👍🏼