Brass is good for spacers on the wrist pin, as it is more soft than steel is. It is used a lot on engines, especially the old vintage engines.
The problem with 2 stroke engines is ensuring the spacers aren't open to any of the intake boost or exhaust ports on the engine. Otherwise you have to use snap rings or C-clips. But with a 2 stroke engine it isn't a problem of course.
Yeah the belt could be a problem to find a new one. Fortunately they tend to last a long time though.
I think some sources like Small Parts might have the belt, but you have to measure and identify it though.
http://www.smallparts.com/b/16411421/ref=iss_16411421
Yeah you could use sealed bearings. They might have been sealed originally, but over the years that went away of course.