First off, thats an excellent price, buy as many as you can.
4cm is a fairly good size, I bet they are mature and flowering (which means tons of seeds!)
I do not believe those are all the same exact lophophora strain... they are at least different types of williamsii if not differnt speices.
Better pics would help.
Lophophora cacti are really easy to grow, much easier than say Aztekium, Ariocarpus, Turbinicarpus or Strombocactus...
Check out some info on growing Lophophora in my cactus thread-
Teotz''s Cactus thread
I'd say if you plan on eating a few, first get a 100% ID on all of them, then grow them strong and fast for a few years, then stress then for a year or two before harvest, the harvested stump will grow new "pups" if you leave a few areoles. I'd say it will only take 2-5 years before ingestion could begin.
In most countries Lophophora is 100% pefectly legal, only the U.S.A. and Mexico (the only 2 areas in the world where it grows naturally) have laws agaist it.