Re: New build, Racer.
It's possible that the speedo is not calibrated to the right wheel size, or that it's getting interference from the ignition. Having someone pace you in a car is pretty good, but they've got to be able to stay close enough for long enough that they're accurately matching your speed - which can be dangerous.
Chain tension: roll the bike so that the top side of the chain run is tight. There should be about a half or three quarters inch play in the bottom side of the chain run. You won't see the chain drooping if it's set this way. Speaking of chain, use some decent chain lube if you haven't already, and a new chain will stretch and/or seat down on the sprockets over time, so check that tension before you ride. (I know yours has some miles on it, but I thought it was worth mentioning.)
Spark plug, start with a NGK B6HS which should be found at any decent parts store. Gap to about .026. I got a fuel filter from a parts store too, but it was associated with a lawn and garden store, not just a chain auto parts store. A metal filter element is better, but paper will do.