It sounds like this is a good opportunity to remain stealth. Problems really start in fifth grade. There is a split in school, as in boys and girls. Up til then, kids are treated the same. If people know you are a transgender, you have a chance at being a male, no questions asked. Gym would be a problem, but if you can get your parents to write a letter to get you out of gym for some reason other than you are a transgender, that won't be a worry.
You have a hard choice to make when it comes to dating and friends. Once you out yourself to anyone, its going to get around. People tend to like gossip, and being a transgender would definately make for good gossip. If you do want to date, its risky in highschool. Both guys and girls get intimate, not as in sex but in touching. If you don't go further than a kiss, the girls would wonder why, and the guys might think you are gay. This doesn't always hold true, but you would need to be careful.
The other problem with telling a girlfriend is that if you breakup and it was a bad breakup, the girl might spread your status around. Usually, I think that if you are dating, then the girl needs to know,, but at the highschool level its a tough call.
You will work things out. If you are having small problems passing, remember that some cis guys develop secondary sex characteristics faster than others. Not every guy's voice drops until later, and they may retain an androgynous look to them for a while. Anyway, you are in a good position to be stealth and I hope your success continues.
sam1234