How many should I apply for?
EACH AND EVERY ONE!
Some give out graduating scholarships meaning simply that they may start out small and each time you re-apply and/or receive anything from them, and please understand it may not ALWAYS be money, you go up the “ladder” as it were toward larger awards. Some give out little or no money but are very good to have on your resume! They may cover all your books – paper supplies, special lab needs, auto stipend, housing allowance, food and/or a grocery stipend and on and on.
Case in point - several years ago an international poetry organization gave out no money but would publish your poem. When they re-published they would send you a form requesting the right to re-print your Poem. As soon as they re-printed you might be able to receive royalties or at least be able to put on your resume that you were an internationally published Poet. (NICE THING TO HAVE ON YOUR RESUME).