4 questions about toothbrushes

Hey there everyone! I have some questions about toothbrushes.. so if you can answer them... Please answer.. 1st: Is it fine to use one toothbrush for a whole year? 2nd: If it isn't fine, usually how long should you stop using a toothbrush and buy a new one? 3rd: What will happen if you use a toothbrush, like for example you can just use one toothbrush for a month, what will happen if you go over that? Will it not clean your teeth so well? and last: Is there a difference between toothbrush brands? Like are there some toothbrushes better than others... Thanks everyone who answered! Happy mylotting, too all!