To answer your questions....
1A) MadCatz Fightsticks Tournament Edition are the de-facto standard for the fighting game community. They were created several years ago by MadCatz with a lot of input from some prominent fighting game community members (MarkMan and S.Kill iirc). Thus, they were created by fighters for fighters. The previous king of fight sticks I believe was the Hori HRAPs before MadCatz showed up.
1B) The WWE model is the cheapest incarnation of the MadCatz fightsticks. WWE costs 20-40, the standard edition (SE) costs about 60-80, and the tournament editions (TE) run 100 to 120. For someone who is just starting out, you would want the absolute cheapest version to see if you actually like it before investing more time / money into it later. I believe the only difference between the WWE version and the SE version is that the WWE version has some ugly art in the front of the stick and ugly button colors, which is ignorable and easily replacable.
2) If you're not a fan of Sanwa, you can try Semitsu. They also make high quality arcade sticks and buttons. Other than these two, I don't know of any other high quality sticks / buttons you can throw onto a MadCatz and still have it be good
3) To give you perspective, this is exactly one of the sticks I own (Xbox360 version). I paid $70 for the stick brand new, and after a few months of use, bought button replacements. I only replaced six of them so that costed me around $20 to $30. Amazon has these buttons for $18 now apparently (
http://www.amazon.com/Green-Sanwa-Push-Buttons-OBSF-30-G/dp/B003D8897M/ref=sr_1_1?ie=UTF8&qid=1378578087&sr=8-1&keywords=sanwa buttons). The Sanwa stick itself costs $25 brand new. But remember, I had brand new parts, bought it when it first came out, and you're buying just now used, so I dunno what your valuation for that would be.
Bottom line:
Buy a WWE Fightstick, and pay $40 brand new but you may or may not have to replace parts later which can cost you $25 for the stick and $20 for the buttons
Buy the Craigslist stick and pay $50 but no guarantees the guy isn't lying about the parts or stick, and you don't know how much abuse the stick has gone through with the previous owner.