I suck at 7 key. There are still 5 key songs I can't realy pull off, so it'll be a while before I can get really good at this game.
Pop'N Music and Keyboardmania are the two I'm not really into, but I might get a generic Pop'N music controller just to be able to play it - I have most of the games...
As far as your controller goes, it's actually better to go with 3rd party because of the major price difference. I mean, the best I see the for the real controller usually is $70 or so. But yeah, don't worry about it breaking down. Just play and have fun...
...and I might sell my copy of Guitar Freaks 3rd, just so you know