1) Installing TBP is quite simple. Install the 'final' version first (Link
), and then unpack the Zathras upgrade on top of it (Link
2) The fully upgraded game supports all of that. TBP itself is mainly focused on single-player, and had some bugs that prevented multi from working well, but the Zathras upgrade takes care of that giving you both singleplayer, coop and PvP.
3) They're available to play against
, but you to my knowledge can't pilot them.