Hello Dex,
Congratulations on getting to this point. I know it's difficult to face all the potential problems but I think you'll be amazed how much of a relief coming out actually is, even if the outcome is less than ideal.
Sounds like you have carefully considered various options and your current situation. Others will have additional advice or experience, but my recommendation is do this at a time when your parents have the opportunity to directly communicate their response without delay. They may want to ask questions that are difficult to predict - not as a bad thing, but because they care. Once you have made up your mind to do the right thing, why wait?
Your school situation is a challenge, but you have an entire lifetime ahead of you to experience your world to the fullest and best extent possible. In the long term you own and drive your future. Being open about who you are can enable opportunities to creatively adapt and find ways to make this work.
Best wishes. I think you will do great.
Kendra