The T stands for Tank. It's a tank system, no filler, no cartomizer as such just a clear plastic housing for the liquid and a special tank atomiser. If they cost the same where your ordering as the non tank kits then consider them, as they give you another option for delivery method. Be warned though, there are plenty of people out there who have had constant leaking issues, flavour loss and others with tank systems, I count myself among them and would never use them again or really recommend to a new user. The flip side to this is of course some people swear by them.
The diff between a 510 pen style (also known as the Joyee 510) and an eGo 510 is really down to looks and battery life. As a general rule the eGo will last much longer, maybe perform a bit better (though that's arguable really, they are both 3.2 volt devices and should perform about the same) and is slightly better supported with eGo specific things like mega ego cartomizers, giantomizers, cones and even variable voltage switches (don't quote me, but I've never seen a VV 510 pen style switch or bat). Then only downside (if you count looks as important) is the ego is a lot fatter then a pen style and looks not much like a real cig.
Regarding cartridges, most starter kits come with these, either blank or pre filled. If you get blank you'll need your own
juice to fill them (recommended to be honest) they are easy to fill, but can be a pain as you'll need to refill often and carry juice around with you all the time. Consider some standard resistance cartomizers (or CE2 clearomizsrs for better flavour) with your order to reduce the need for atomisers and cartridges at all.
Whatever you chose, as a starter kit the eGo or 510 penstyle is a great choice, Happy
vaping!