No one plays on xbox, and with the constant updates on PC it's still a modern, and fantastic game. Valve will probably do Half Life: Episode 3 long before we see a new Team Fortress, and even then, get it on the PC.
Try trouble-shooting for steam if you really want to play TF2 (which I suggest) since it is worth it.
TF2 doesn't really NEED mods, but there are some out there. No zombie mods I don't think. The gametypes and maps are fun enough to not need major mods.
garrys mod will be fine as an extra to having the orange box as a whole. --- garrys mod needs to come to mac!!!!