Re: New build, Racer.
Welcome to the forum, and don't take this the wrong way, but ...
Call me unconvinced about your speed estimate (unless you were going downhill). It takes quite a lot more than a stock kit and sprocket to do 45MPH with an HT motor. Still, I'm guessing those are 700c wheels, which would give you a bit more top end than a 26"er.
In the top pictures, I see that the stock air cleaner tubes are pointing up. Those should be down, like in the last picture, to keep road trash out. The other thing I see is that the chain is way too loose. Snug that up before it jumps off and throws you down like a rag doll. You might invest in a fuel filter, because the cheapy plastic one on the inside of the petcock is junk.
Apart from those few things - nice clean build. I've got a build going on a similar bike, with those flat bars - do you get a lot of vibration through those? Mine seem to be pretty harsh.