Blood Bowl is one of my favorite games of all time!
One of the great things about nit is that you don't need a whole mess of models to get started, 11 players and a coach gets you in the door, a team of around 20 or so minis is already pretty substantial.
The box (which used to cost $ 40) is 3rd edition, which is as far as BB ever got, anything beyond that were 'update' downloads, Journal articles and house rules on the web.
GW still sells (most) of the teams, and you should be able to find them online various places.
Failing that, converting minis for BB isn't hard, just cut off the weapons, do perhaps a little bit of surgery on the rest - hey presto, a Dwarf Blocker!
It isn't, however, in any way similar to American Football, the game mechanics are much more closely related to Rugby or Soccer.