The miniatures on the checklist are all of the miniatures that came out for that set. Each of the three sets out have their own checklist. You have to buy Booster Packs of more miniatures to get there. Where you bought the game itself ought to have the boosters as well. As for the maps, I fold them in the opposite direction of their crease and they stay perfectly flat. All it takes is a few folds. There’s other maps out there, and you can start with the Wizards of the Coast website: they release scenarios and new maps to play with every month I believe (maybe it’s every 2 months).
To find a bunch of maps and other forums that discuss this game, Click Here. That’s where alot of people get their new maps. I’d suggest getting a second Starter Set just to have enough maps, since the 4 they give you isn’t enough to play on (in my opinion, but we also play 150 to 300 point battles instead of 100).
I hope this helped some.
-=Grim=-
Edit: Just to clarify, I mean that each set has its own checklist of totally different miniatures. Set I, II, and III all have completely different (but compatable) miniatures.