Measure your chainline.The new wheel will be 42mm,so if you're within 40-45mm you'll be fine.As far as the chainring, the inner will probably be better(again chainline).If you like the gear you're running now and if the chainline is good just get a cog with the same toothcount.I'm guessing your chainring is about 40T and the cog you're on is 15 or so.That would be a 72 inch gear wich is not bad for fixed.What bb you'll need depends on what crank you'll buy.