The Chinese kits are actually as quiet as the 4 strokes with the stock muffler. The harbor freight motors are great but require a lot of engineering to adapt to a bicycle and probably not a good idea for a first build. The China motors vary substantially in power and make more than enough to make your bike go far faster than it should. Dax will get more recommendations on here than any shop/store and there is a reason, he will help you beyond the sale and his products are excellent. One of his 2 stroke kits is arguably the best way to get into this hobby you will find. The week point on your bike is the rear hub, I build on that hub all the time and you MUST disassemble it, check the shoe alignment and engagement contacts then FILL it with high temp automotive grease. Then it is a gem but without doing that it can be very dangerous. Also if it has fenders, remove them, they are also very dangerous. Take a look at some motorcycle fenders, unless you are building something comparable they will fail, jam your wheel and you can imagine what will be left of you and your bike. I do what Dax does but just for the local Tucson market and build performance motors and top ends for one of the online companies. I am more than happy to help with any questions or things you may need for your build just P.M. me I know those bikes very well and love them.
Happy Motoring!!!