On accuracy, the Yugo SKS generally does 2-4moa, which is the military standard. Most civilian ARs can do 1moa but only the most expensive ones guarantee it.
A zillion people here could basically tell you WHY to keep your Yugo SKS in stock configuration, but the basics are this:
Adding a folding stock usually makes it clunkier than the original wood one. To me, adding a folder makes no sense when you have a 20" barrel. 16" barrel ok.
The original fixed mag is super reliable. Anything else is a gamble. It can be a calculated gamble if you buy a few detachable mags and try to make them work. No kit is required, but in my view the only reason to use detachable mags on an SKS is to use a full length scope. Instead I'd just spend the extra for a high magnification compact scope.
If you want to add a scope, make sure it doesn't block the stripper clips from feeding. And don't trust the mounts that just slip on. At the very least, use the Leapers mount with the screws that tighten on the receiver.
The Yugo SKS is a great rifle. In most folks opinions it's best used as it is, though a small mod here and there can be good. Before getting into any mods, look at the economics. If you want to get into detachable mags ($20 a piece), a folding stock ($50), and other requisite US parts (to comply with import laws), consider an AK variant. Detachable mags are less and some features you want on an SKS are either standard or work much better. If you want a compact, folding stocked carbine, the AK is far far far better handling than the SKS, especially the heavy Yugo.
My suggestion is buy a Yugo and try it stock, and see if you don't fall in love with it the way it is.
