Any MTB wheelset will work, there are none specific to the 4300 (or any other bike that I know of). Just get a 26" MTB wheelset and you'll be straight. As far as tires there are a lot of slick tires made in the 26" size for exactly what you want to do, ride MTBs on the road. The slicks will save the knobbies on your off road tires and also offer MUCH less rolling resistance.
As far as a new rear cassette.. Either pick up a cheap 8sp cassette from online or your LBS, or I personally would hit up eBay. You can get a SRAM PG850 like what came with your bike
for $22 and Pricepoint offers some decent inexpensive machine built wheelsets as well.
Personally I'd take whatever wheelset you buy and put your offroad tires on it and put your slicks on the factory rims as whatever you buy is likely to be better than what cam stock on your 4300.
If you got the disc option you'll also need a new rotor for your spare wheelset and make sure to buy a disc compatible wheelset..