I think it's a great idea. For powder/groomers, I would go with 4FRNT MSP. It's a super versatile ski, and it's got a width of 96, so still floaty in pow. I've heard super good things about them, and I have a friend who rides them and absolutely loves them. I ride 4FRNT switchblades, different ski entirely, but I'm very happy with the quality.
as for the park, if you're gonna buy used its mostly dependent on what you can find. Just don't buy line.
I have a pair of Nordica Ace of Spades, they're pretty good, and decently flexy. my switchblades are super nice, and a little stiffer, which is what i want for jumps. i hear atomic punx are sick, and armada makes some quality stuff, halos and ar7 for example.
hope this helps.