I recently had a multi-speed bike built up from a frameset that has forward facing dropouts. I've been interested in trying a single-speed for some time so I'm considering making the investment in new parts to make my bike a part-time SS.

For economic reasons, I would go the route of removing my 9-cog cassette and using spacers and a single cog on the rear. How much of the "performance" aspect of a SS will I be giving up by going this route as opposed to a dedicated SS wheel? I know it will weigh slightl more but will be the only real penalty?

Also, are there SS cranksets that use an external bearing BB? This would greatly simply things.

Would a conversion be as simple as replacing the casette as described above, replacing the crankset and stripping off the parts that are no longer needed? I would have my LBS do the actual work since they've been building SS bikes for close to 20 years but I want to do my research before getting that far into the process.