I agree with the above. I highly recommend you do at least one rotation as an MS4 in both dermatology and pathology. They are very different & you do not want to be stuck in a residency & later regret it. Pathology is 4 years (if AP/CP). Dermatology has a preliminary year in which you will do clinical months. Part of me does miss seeing patients, but I honestly would prefer interacting with my colleagues and clinicians.
The typical residency program may seem like a joke as compared to some other fields (i.e. surgery). However, there is an incredible knowledge base that must be learned during residency. The field is just so broad! It's almost like drinking from a fire hydrant. One can quickly get submerged in the daily grind of grossing and so forth, but you have to be disciplined to not be a passive sponge for 4 years. It's not just about passing the boards.
My hours during residency weren't bad at all. Like sirenomelia said, typically 8-5. Your first months on surg path will be grueling, but you will become (I hope) much more efficient. I personally loved surg path so I didn't mind. Call is mostly from home. I rarely got called in to do frozen sections late/middle of night since we have a busy transplant service at my residency program.
Dermpath, as you already know, is competitive. I would recommend that you start doing some research projects once you start getting comfortable with your first year. Try to present (oral or poster) at the ASDP, USCAP, etc. Publish a paper or two. If your home institution has a fellowship program, get to know the director, be present for the lectures, read, and do well on your rotations. It also doesn't hurt to rotate at outside institutions that you are interested in applying to. Develop a relationship with a mentor(s). The typically drill for anything I guess. Personally, I applied to 22 dermpath programs & got called for 10 interviews. I went on my 3rd interview, got accepted, and cancelled everything else. I was very lucky!
As for as I know, there are no combined pathology/dermpath programs. Also, although you may have an edge at the home institution, it doesn't guarantee it. Regarding money, I have no clue. Dermpath will be my second fellowship (surg path the first) so I'm hoping that I'm a relatively qualified candidate, but I also would prefer to work part-time since I have a growing family. If you are interested in academics, of course, the pay will not be as high as you expected.
Good luck!