good choice on the wheel upgrade. those IRO wheels should last you a good nice smoothe-rollin' long time, especially compared to the stock ones that came with the bike--which, by the way, may be very nice for the occasional four weather ride!
if you go fixed (and i recommend you try it!!!!!!!!), tony from IRO recommends using a good cog on his wheels. i don't know what came on your motobecane but i'd recommend getting a dura-ace or eai cog (or surly or soma or a few others people may mention). cheap cogs have a tendency of f-ing up your hub's threads. same goes for lockring.