- By the time you replace rear wheel, cranks, pedals, seat, post and grips you're already into this bike a good deal more than what they're asking for it, which isn't a solid deal anyway. Save your money.
- Welds weaken steel (with the exception of high-end exotics like Reynolds 853 or True Temper OX Platinum), and this smells like a hack job anyway...2 strikes against. Pedals are not designed to be welded to crank arms, and this joint will fail sooner or later, I can almost guarantee it.
- If you change your chain regularly it will not damage your sprocket/cog. Measure 12 links with a ruler, a new chain will measure exactly 12". If the chain is stretched past the 1/16" mark, the chain should be replaced but the sprocket/cog will likely be undamaged. If it measures past the 1/8" mark you MAY be wearing out teeth. The only way to know for sure: put a new chain on...if it skips, you're into it for another couple bucks replacing sprocket and/or cog.
- I wind up having to replace my road bike chain every 2-3 months, FAR more often than Beerman replaces his BMX chain. It all depends on how often/hard you ride. Just because I'm not thrashing around on my road bike doesn't mean it's leading an easy life.