Those reviews that WhiteFang does over on Eurobricks are great. They're essentially the best reference out there (that I know of) for the CMF line, and I think he's done every series - even the rarer ones like the UK Olympics team.
As for distribution, I do think Lego has gotten better with this as the series have rolled on. For years you could count on the costumed figures being (tied) for the rarest in the box, but that has started to change recently. The vast majority of the series had three full sets in each box, and then some extras. I'm almost certain this has been true for all the licensed lines, even Disney. I haven't gone to double check my memory, but I want to say that Lego did three series in which there were only two sets in a box - I'm going to say that was series 9, 10 and 11. Series 10 was the absolute worst experience (pictured a few posts above) with six figures that only came 2 per box, and then four figures that were 6 per box. Now, they could argue that one would army build the soldiers, and maybe the baseball players, but no one army builds mechanics or skydivers. I think I've still got 30+ of those stupid blue skydivers sitting around! I've always been very thankful that they went back to three full sets per box, but the days of 2 figures per box is on the horizon if reports of a 22 figure Harry Potter series turn out to be true.