If you're just at 200 miles and it's reliable...running trouble free.... I'd put a few hundred more miles on it before creating issues. Enjoy it for the time being. It looks like you put together a really nice bike. I'd work on keeping it that way as long as I can because the time will come when things start to get out of whack...especially if you run it hard a lot.
You will have plenty time to increase performance in the days ahead. Smart thinking is greasy hands and busted knuckles can wait a bit.
I know it's inevitable...the mods will come. Just try to get some enjoyment headache free for a bit.
Concentrate on making sure your wheels spin free & true....brakes working free and well... perfecting sprocket true, chain alignment. Make sure there's absolutely no air leaks. General tuning that's necessary anyway. Things like this increase performance and do not dig into your wallet. Performance increases come in small increments over time unless you spend a fair amount of money on it.
Hopefully time will teach you how to recognize when your bike and engine are happy and performing well or not.
When everything is correct, a 66cc engine pulls a bike very well.
No matter what you do, safety needs to be the first and last thing you think about every time you get on to ride. Make absolutely sure this ride will not be you last ride.