Personally I wouldn't replace the crankset if the original works fine. In fact I'd prefer to ride the bike as Schwinn intended - the way you rode it all those years ago, OP. The bike will never be a lightweight racer so it's pointless to get rid of the one piece crankset imo, which will be a fairly expensive endeavor. I'd get it all back together once you're done with the powder coat, and replace the wheels also only if needed. You'll have your bike back and ready to ride w/o a major investment.