Ideally I should apply to as many as possible. However, I am applying to some research programs and they ask for letters of recommendations or reference forms. I want to be safe and apply to more programs/internships but I also don’t want to annoy my professors and ask them to fill out so many of these forms/mail them out. How many of these summer programs/internships should I apply to?
Also, if I want to use one of my professors that wrote a letter as a reference, should I notify/ask them in advance or can I put them down as they have already written a letter?