BellaItalia

I bought a great road bike this past fall--Litespeed Bella, drivetrain upgraded to Ultegra--and now that the weather is messy and the roads often icy or at least wet, I don't want to do my 25-mile (roundtrip) commute on it (both because of the damage that would happen from the salt/sand/wet and because the narrow road tires are so prone to slip on wet/slick/sand-covered roads). So I mentioned to my son, who has worked at REI and is an engineering student and loves bikes, that I wished I had a cyclocross bike like he does. He immediately offered to build me a bike, buying a cross frame off ebay and salvaging some parts off my old Trek 1220 roadbike, and buying the rest. We found a 4-lb NYC Bikes alu frame, bought it for only $50, and are embarking on this project.
The rear spacing is 135 mm. We've ordered a fork w/ cantibosses and a pair of Avid Shorty 4 cantilever brakes. We're trying to decide what kind of wheels to put on. If it makes more sense to put more money into only buying a rear wheel and salvaging the Trek's front wheel, we could go that way--but would a matched wheel set make more sense? I noticed Nashbar or Supergo have Mavic CXP 22 rims w/ SHimano M475 hub w/ the right spacing for $120 (marked down from $199, and using the current coupon), or Mavic Open Pros for about $180. My parameters are to make this bike as much fun to ride as possible while not spending too much (I splurged on the Litespeed!) and making it one I'd be willing to expose to bad weather.
My old cassette (7 speed) and chainrings are kinda beat, so we're looking at replacing them, altho salvaging the cranks. We'll also keep the STI brakes/shifters.
Any advice, particularly on the wheels? And good grippy tires? Any general advice on pitfalls of this kind of build project would also be welcome.