Unfortunately , there do not seem to be many people willing to spread their experience and knowledge of the game to new players like you and I. I posted a message trying to learn more about the game and had many views but few actually responses.
It is a shame since that is the best way to nurture and expand the game.
I'm quite positive that most views are other curious people who couldn't answer your questions. The few replies you got were probably the majority of the core posters. There aren't alot it seems.
Anyway, F1fan, I'll give your questions a shot:
(1) Axis and Allies Miniatures is a tactical hybrid of a traditional tabletop wargame and standard boardgames. Each player builds and army based on an agreed number of points (the standard armies are 100 points, but it seems that alot of people here ignore that rule and go for bigger armies), one side being Allies and the other Axis. The units are represented by excellent prepainted game pieces (in my opinion they're excellent!). Each unit has a corresponding game card that details it's abilities, such as how effective it is at certain ranges versus enemy armor or soldiers, how well it defends against attacks, and other rules bits. Each player takes turns kicking the hell out of the other side until one side wins, which is usually determined by holding key objectives represented on the map.
It's actually alot of fun.
(2) All you *need* is the Starter Set, which contains the 4 maps you battle on (maps = game board), dice, enough units to play the game, and the little details like the cards and counters. Now, you only *need* that, but you will *want* more... seriously, just the Starter Set is very limited. You'll want a few extra booster sets to have more models to use, which means different tactics and play. Also, you might want to invest in a second Starter Set: one set has enough maps to play on, but it's too small
! An extra Starter means another 4 maps to connect to the board, allowing for large maneuvers and deployment and a helluva lot more points on the table!
(3) Some game stores sell singles. Ebay does too. If you Google for them you'll find a decent amount of online stores selling pieces. Some people here, myself included, are down for trading amongst ourselves too.
I hope this helped some.