The FM is a ton of fun to play. And I wouldn't say she's overpowered, although most people will lose to her the first few times they play because her playstyle is so aggressive. Certainly she's considered inferior to an earth wizard build, which includes a core set mage and a lot of cards that come in the FM v WL set.
I'd recommend the second base set. It's a little more expensive, but the second board, the extra dice, and the extra spellbooks are worth it in my opinion. Also you'll have enough status boards and counters to play 4 player if you want.