Just picked up a set of wheels with a flipflop hub today. I've been riding with a surly cog loctite/jbwelded on a freewheel and wanted to get a flip flop in case my legs wear out on me. I've been riding 42-16 with some ease for a little under a year. These tires are lighter and thinner than my old 27's so now I'm wondering about the cogs I should get for these wheels. What brand should I use? (I won't be heading to the velodome but I do use my bike as my primary vehicle) Should I run something higher? lower? Does my freewheel side need a smaller or larger or different cog or is it all interchangeable? Will spacing the tires be a cinch or should I set aside many hours? Any suggestions for places to get good deals on these cogs?

If you have an answer for one or all of these questions I'd be a happy man.

Thanks...