On top of this, make sure you give nothing in-game and accept it as donations only. If you accept the money from donations and give something in return, then you are offering a service and are considered a business. All donations in order to be legal and not heavily taxed to you or your parent's income must be put back into the server. There are also a lot of things that are very specific about this. The IRS and Mojang offer information about this and also just google your states or countries donation laws because it may vary.