I have picked up quite a few nice MTB wheels used cheap. I would look for some wheels with Deore LX or DX hubs. I have two Trek 950s myself. I have put 1.25 inch slicks on both of them. One is a 1994, the other is a 1992. I use two sets of wheels for mine, one with slicks, the other with trail tires.
I am running 7 speed right now. I don't see any reason to go with nine speed, even though I have the parts. There's lots of seven speed stuff out there.
Here's mine with slicks:
And on a recent trail tour: