I can give you a fair amount of guidence if MD/PhD is what you're going for. I applied to these programs last year and therefor have done a lot of research on them. I didn't have your stats though and so they didn't give me the time of day.
Brief Outline:
When submitting your AMCAS, it will ask you what program you want to apply to. Select MD/PhD and it'll require another essay besides your PS where you have to outline what research you've done and it's significance (10,000 c. limit last year)
Most schools will consider you for the MSTP / MD/PhD program FIRST. If you're granted an interview, at most schools, this will be a dual interview for MD and PhD (and some schools even pay for your expenses!). If accepted MD and PhD you're good. If you get rejected PhD, most schools will offer you the MD acceptence only and you can always apply into the PhD half of the program once you're attending the school. If you get rejected before the interview, most schools turf your app over to the MD only pool just like the rest of us. Some schools do it backwards. First they look at you for MD. If rejected, that's the end. If invited for an interview, they'll forward your stuff to the MSTP program and htey'll look you over. And then there's the schools that are just wacky
Theres two types of programs. MSTP = Medical Scientist Training Program. These are NIH funded and extremely tough to get into. Everything is paid for and some give you a living stipend. MD/PhD programs are just that, you do 2 years of med school, 3-4 years for your PhD and then youre 2 clinical years. These aren't funded by NIH but may still be funded by the school. Generally you'll still pay for Med school but during your PhD you'll be a TA and get paid. All the funding stuff depends on the school.
As far as competativeness goes, I'd argue they're more competative. Yes you have less people applying but there's also very few seats. The highest matriculant number I've seen is 16 I believe at UPenn. When there's only on average say 6 seats to fill, you've got to make yourself seem like the holy grail to get one of those seats, even if only 1000 people are applying.
Any other questions feel free to ask! There's also an MD/PhD forum that can be helpful