I agree that Pricescope is a good site. It will certainly educate you if you have the time to put into it. Keep in mind though, that it is primarily a diamond dealers site (and an American one), so if you turn up asking how to wipe your bum, you won't get much traction, as such
Having got some clue, and asking very specific questions, you will be helped with invaluable 'trade' advice.
The 4C's are nothing, just a marketing exercise. There are certainly 20C's - depends how deep you want to get into it. I mean a stone could be top of all the '4Cs' but an absolute dog because of graining or fluorescence, and so on...
I get my rocks (or, er, rather the wife's rocks) FedExed in from Texas. Much better value for money than buying locally (certainly half the cost of ... what's the local jeweller called... SooKee... Pookee).
Forget Larry Jewellry. I don't want to pay several thousand in premium to be 'stroked' by some sales assistant for 2 minutes. sheesh!