There is no universal answer to the "how many schools" question.
On paper, you look like a good applicant, but I would suggest that you take a good, long, objective look at your non-tangibles before you come up with a number. Is it easy for you to talk to people? Are you a confident and competent writer? Have you bonded with faculty members who are likely to write glowing recommendations for you? Have you really taken the reins on your current research projects? Do you radiate excitement when talking about science? Are you good at explaining your projects to non-experts without losing them?
If the answer to all of those questions is yes, then you are likely to be an all around great applicant, and you can probably apply to 8-10 schools fairly safely. If you are lacking in any of those areas, tack on a few extra schools. If you are lacking in many of those areas, open up a new credit line, and apply anywhere you can. There is no reason to sell yourself short by applying too narrowly, but there is also no reason to throw your money away on places you don't like because of some misplaced sense of self-doubt.