Hi mpahopeful,
Regarding you questions:
1) I believe the admissions process for the MPA/ID is VERY competitive. I applied to 12 programs and this was one of the only 2 that rejected me. I might be wrong but I seem to remember that the class is pretty small, 70 or less. They are looking for people with strong quantitative training + a gre over 161 on quant + professional experience that prooves your dedication to development. Besides being relevant, it is preferable if your professional experience shows your potential.
2) The student body mmmm I dont know exactly for I have not meeted them but I guess, because of the admissions process, they have great profiles.
3) The mayor pro/con is that this program is the most quantitative one you will find. It is not just the question of whether you like math or not, some classes seem to have a phd level. You should think carefully if this is what you are looking for.
4) Very well reputed. In my opinion,it is the best HKS program. Not that it matters but it was in my top 3.