There is one thing, the Healt pool. You cant increase it a lot. I mean, you can wear gear that increase it, but at heavy cost of DPS. How its the end game? Ive seen some mobs at the edge of the maps (Lairs, or semething like) with more than 20k each (if i do remember). If you dont gain "levels" on this game, how to improve, efectively, the HP without messing up DPS?
Lairs are the TOR equivalent of H4 Areas. You're not supposed to solo those.
As far as stats go, in the end game you have gear that has nothing but one stat, so you can have just as much hp as you think is appropriate for a fight and that's one of the tricky and interesting parts of TSW. You don't have set gear, just the QL of items go up and the stat in the goes up. When I solo, I use 2 items with nothing but HP on them as that gives me enough room to survive even the odd bad pulls or mobs with nasty abilities without having to shuffle my build around, even though I have every skill unlocked in the wheel, so I certainly have options.
My favourite build is Assault Rifle/Pistols with pistols givin a single target builder and a resource dump while AR gives AoE and Red Mist. The build revolves around massive dot application and other passives which cause massive buffs against targets with dots on them in addition to Live Wire. It's a solid build that can handle anything apart from some mobs which reflect dots, those lurkers in Transylvania are nasty for DoT builds. For them and other anti-DoT mobs, I change dots to Auto-crits when I penetrate and replace my AR with Blades.
The main thing though, is to look at ALL the wheels, and ignore the mentality of using blade passives if you use blades. Elementals and shotguns have some seriously awesome passives for any DPS build.