Given your weight, i would suggest getting a set of wheels from IRO. They can space them to 126mm for you, so you don't have to worry about it, and if you call, they may be able get 36 hole rims. Tony is good about custom orders. Well built 32 spoke wheels should do fine assuming you don't have many potholes or really rough roads on your ride. If you want to get a bombproof set of wheels, get the velocity deep Vs or the Mavic cxp33s. You'll spend extra, but you'll get really strong wheels.

As for the gear ratio, since you have a road bike now, pick a gear and ride your commute without shifting. When you find one you like, add a tooth or two to the chainring, or drop a tooth from the cog (to account for the lighter, more efficient drive train) and there you go. Alternatively, the best advice I've seen around here is to start from about 70 gear inches and adjust from there.