If your Puch is the 1 speed, the crank main bearings are easy to find at any shop that sells bearings. Same with the two transmission ball bearings. Seals are also common stuff.
If it is the 2 speed the crank main bearings are not so easy to find. I believe that the 2 speed is also inherently noisier, at least at low RPM. I am refering to engine noises, not exhaust noise.
The first thing to check after pulling off the cylinder would be the connecting rod. If it has end play you are kinda screwed, since finding a "rod kit" is not easy and it also requires a press, dial guage and jig to replace the rod.
The exhaust should not be objectionably noisy unless the two baffle components are missing from the muffler. They would simply need to be replaced.
The horn is not very loud no matter what and not much you can do about that. The only reason the carb should be contributing to your noise is if you are refering to intake noise, i.e. the "wah" sound due to the lack of an air filter/box to sufficiently suppress the noise.
If you don't already have it, you should get the service manual such as the one at: