I've got almost all the parts to replace the flywheel, PP, and clutch; I just started reading about the flywheel shims and crank end-play. Do these need replacement ? Where are they sold ?

I can't say that I've seen it recommended to replace them, but you might need different sizes than you currently have in order to set your end play. Keep in mind that you have to use three shims.

I know AA sells them, the Bird might but I didn't see them listed when I needed them last year. I'm sure the more knowledgeable out there will have other sources.

http://www.evwparts.com/volkswagen/Type4Flywheel.html
found this, if it helps

jim, if they are not wore out, thinned, or cracked they are reuseable. im sure european motor works has them. if not, let me know what sizes you need.

Thanks. They sell .24 mm, .30mm, and .32mm. Since the old flywheel hasn't been removed yet, would I decide on which shims are needed after removing and fitting the new flywheel ?

Not sure here...

Correct, you won't know what you need until you fit the new flywheel with a a set of shims as a starting point. You then measure the end play and adjust shims accordingly based on your end play - too tight reduce the total thickness of the three shims, too loose increase the total thickness of the three shims.