Yeah no decomp in the usa.you would see a cable running to the head next to the spark plug if it has one. Your missing alot. Worry about the engine first. It's safe to say that even if the main bearings are ok, the seals need to be replaced. So you'll at least need an engine teardown
Everything is available for these bikes. If I were you I wouldn't worry a lot about original switch gear and buy one of the many available sets from treatland.tv/doscycles.com. kill it just a wire to the coil that grounds it so super easy and keep the lights hardwired to on.
As for speed and such. A 14 or 15mm bing carb would be a nice upgrade, as I imagine that bike has a 12mm bing. If you do, don't forget the bigger intake or it won't help at all.
Cylinders are available up past 70cc, and many are direct bolt on and will really help with performance. Just remember that it's a two stroke, so carb jetting is very important. If you change anything from the carb thru the engine to the exhaust, you need to jet richer or you risk seizure.
If you want to keep the engine as is after fixing it up, consider a mild expansion chamber exhaust. The exhaust is super important for two stroke power as it's a resonant system. You can expect a few mph from an exhaust and upjet.
Find out what speed model you have! They made 20, 25, and 30mph bikes, or more accurately 1, 1.5, and 2hp bikes. If it's a slow bike you'll at least want to get it up to 2hp stock configuration.
As for the seat, clean with soap and water then apply some sort of vinyl conditioner. Your just replacing oils...don't tell anybody but I use mane and tail hair conditioner. Works great! Apply thickly and let it sit for several days. Wipe off the excess.