Well, there are 16 programs in the country. Each program has 3-7 slots depending on its size. My estimate would be that there are about 16-20 slots each year available.
Some programs do require research and others do not have such emphasis. All programs are structured 3 years programs and I believe are all quality programs.
As far as COMLEX scores, I don't think there is any published data. Higher is always better. I don't think there exist a DO match for derm. You will need to apply to each individual programs.