I think all of the doubts and concerns you wrote are really normal to have before a surgery like this. Try, and always push the negative thoughts away, and think of the bigger picture; in the end the journey will be worth because the destination is freedom.
It's impossible to really prepare for something this big, but when you feel overwhelmed just try and not think too much about it, take it step by step, and it will evolve naturally. But honestly, asaide from having fears (which is normal), this should also be super exciting for you. Remind yourself of that. Good luck, and hope you can get someone to be there with you. Sending you tons of good karma.