I bought Albion prelude, Reunion and Terran Conflict but i am wondering which is the last in the series. Do they extend themselves and can I install/play them all at once? Other then that are there any free DLC's/mods I should install on top of it? I vaguely remember there was a free add on pack that adds some more items etc.
Reunion was the first X3 game; Terran Conflict, the second; and Albion Prelude, the third and last. I would not recommend playing more than 1 game per 2 arms at the same time.
You can get the official addons called Bonus Packs from Egosoft's website – they add various command options for your ships