Bicycle Mechanics - Newbie builders seeking advice

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.

Matching your front wheel to your back is like matching your purse to your shoes. It may look nice, but it isn't going to make your bike go any fatser (or ride better, or whatever).

I'd try and run old stuff, since it's going to get screwed up in the weather anyway. If you're going to buy new, get cartridge bearings. It's easier to pop out a cartridge than it is to regrind a bearing cup. I'd also keep the old drivetrain unless it's dangerous. It's gonna take a real beating in the salt and sand. I'd think about going single-speed, internal, or even fixed, especially if you have any fondness at all for your deraillers or STIs.

Tires are funny. Basically, high-pressure slicks are best for everything except mud and slush so thick that your skinny tires can't find the pavement underneath. And maybe those days when there's still a bunch of slush but also an inch or two of ice over most of the road. I've only found three or four days that were so awful I wished I had different tires, and that's in two winters and change of riding every (work) day. Something fat and squishy is what I would pick for those days. maybe even studs, if there's a chance of ice underneath.
For most days, I find that studs (or even knobbies) have enough rolling resistance to be annoying. But they sure do feel more solid in skecthy conditions.

Oh, and you might think about a disc brake up front. Snow turns into ice under pressure (read : under your brake pads). It's like stopping your bike with ice cubes.

You might be able to find something (washers) to use as spacers for the rear wheel. You might get away with just mounting it on the wider spaced dropouts, clamping it and leaving it the way it is. Sounds like a fun project. Good luck with it.

... You might get away with just mounting it on the wider spaced dropouts, clamping it and leaving it the way it is. ... With a steel frame, sure, but with an aluminum frame, it would be far safer to match the OLD as closely as possible.

i commute daily on a fixie conversion, the wheels don't match, and i don't mind, it's just an asthetic thing. i also ride ritchey speedmax's year round, work well on the road, the dirt, the snow, everything i want to throw at them. good, affordable cross tires.

http://aebike.com/site/images/library/catalogs/soc/prodl/TR3144.jpg