I went through the MSTP route and went into pathology. I was told by my program, that nationally, MSTP-ers match into 1. IM, 2. Peds, and then 3.Path in that order. Not sure if that's changed since I graduated.
I don't think my PhD helped me with pathology at all, except in one small part in one subspecialty service during residency. That's it.
As far as grants for residents/fellows, the K08 is the main vehicle for that since you can take that money with you when you leave.
As for multiple grants, this generally isn't possible since most entities that issue grants have a clause that they can be the only funders of a specific research project. So if you applied for won both a K08 and a American Cancer society grant for the same project, you'd probably decline the ACS grant and keep the K08 (although you can still list in on your resume!). While not impossible, it isn't likely that a resident/fellow could have different enough projects to warrant multiple grants. At least not without risking some ethical/legal issues.