How many internships are too many?

Unless you're tight for money, you don't need more than 3/4 internships imho. In fact, even two are good enough. And 3 things matter. In descending order:

1. Your title/what your title said you did. Notice that this is not necessarily what you actually did. Some people have "junior analyst" and didn't open excel once in their internships. While someone who actually did the work will be significantly more prepared for both the interview and the job, resume screeners, recruiters will (mostly) just look at the title.
2. Company. Big name = better. Some astute screeners/recruiters may realize that an intern probably gets more significant exposure at a smaller firm, but most will not. They'll just be attracted to names they recognize.
3. A good recommendation. They'll background check. Make sure you weren't fired.

If you're a finance/econ student aiming to work in finance, stick to finance internships. If you were engineering, highlight the "soft" skills your internships (if they were engineering internships) required. If you were liberal arts, highlight the "hard/quant/finance" skills your internships required.