Ok, here's what I know. I'm sure there are people here who can add a lot more.
1. Every DML kit comes with single link tracks, as far as I know, and a lot come with PE. A Stug III C/D kit I have, for example, has both. DML are also very nicely detailed and have a lot of parts. Look for the fine print on the side of the box, it generally says whether it has PE or not. The only DML I would steer you away from is the PzIVJ - its a real dog.
2. Here's a short run-down.
Pz I - lite training tank
PzII - lite tank, generally fitted w/ machine gun
PzIII - Germany's early war main battle tank, relegated to infantry-support role later in the war.
PzIV - early war infantry-support tank, later up-gunned and armored to become their main battle tank. Chasis was also the basis for many other vehicles.
PzV - Panther, medium tank w/ sloped armor - possibly the best tank of the war
PzVI - the famous Tiger Tank, very heavily armed and armored
PzVI - Tiger II or King Tiger - an even bigger, nastier version of the tiger.
Sturmgeshutz or Stug - assault gun
Nashorn & Hetzer- A/T
Hummel and Sig - tracked artillery
Beob - these were command vehicles, I think
And any thing with a "Jagd" in front of it was a tank-hunter
As for the A, B, C, etc designations, they work much like they do with American combat aircraft. The initial version is A, the next upgraded version is B, and so on. The only exemption to this that I know of, is the Panther. If I remember correctly, the G model came before the D model for some reason. Any help guys?
Hope that helps some.