a) Don't think about that now. I mean it. There is NO point. You haven't even passed the very first of hundreds of hurdles (five/six years in medical school comes with its price, and you WILL be culled).
b) For that you should do your own research, on this forum and on google.
c) There are varying degrees of competition (which is not the same as difficulty, since EVERYTHING is difficult in med) but like I said - don't think about this now. You still need to secure a place and prove yourself as a doctorer.
d) For this you would need to understand the structure of the teaching hospitals, allocation systems and all that jazz. Once more, forget about it until you're in clinical.