In Ranked, that is. I have so many champs for top lane I know how to play, but obviously the more I play the less I play a certain champ, the less practice I get, the worse I do. However, it does allow for variety. So should I stop expanding my top laner pool for Ranked unless I find someone I'm really good at, or should it not matter?
You should have a reliable "main" to pick for when you pick early and don't know what you are up against. If the enemy picks your main, take someone that performs well against them (a "counterpick," or at least another safe one). If your main struggles against some champions, have an alernate choice available.
Given that, you will probably have 3-4 champions for your primary position. You should still play others in normals, so you know more about their kits.
I don't see a problem with expanding your pool. Odds are some of the champions you won't play as much will become comfort picks. Where you don't have to play them all the time but can still do decently with them.
