How many US Colleges should I be applying to?

If you need financial aid, 15-20 is a good number. Otherwise, less than 15 is fine. Make sure you apply to the right schools, though!

There isn't a correct or incorrect answer to this question. The standard way to think about applying to colleges is dividing them into categories - reach schools, target schools and settle schools. Once you have a few that apply to each, you should be fine.

I would echo the other responses and also add that you should only apply to as many schools as you think you can put your absolute 100% into each application - a good rule of thumb would be to make sure that you never ever copy paste anything from one application to the next (except the common app essay and general info etc.) - all the school specific essays should be totally unique and completely specific to the school - show them you care and that you really do love their school - otherwise you aren't going to have a chance