Concerning 3, I'm pretty sure I saw awareness levels sink gradually without blocking the direct line of sight to an enemy.
Also, yeah, I concur with neonesis second point, the hostages stayed in captivity in my melee/subterfuge/crafter playthrough, because I was too weak for a direct confrontation and there was no proper stealthy way to terminate the raider leader (though I guess had I focused on crossbows instead of melee, Snipe would have made short work of him ). Perhaps add a flag to determine wether dialogue initiation with an object is possible during combat?
Alternatively, add a second, more difficult hack check, with which to exempt yourself from the turrets feasible targets.
Well, it became the easiest thing on earth with Sniper Rifle - it oneshots most enemies, with Snipe feat also the Raider Leader.
I think it's another issue - the low amount of health that PC and NPCs have compared to overall damage output. I often find that who shoots first generally wins the battle, and that one lucky/unlucky roll can turn the tide of the battle.
EDIT: (to avoid doubleposting)
I also feel that Stealth is currently not fitting its role very well. It's like Stealth is somewhat useful to every type of character, just to be constantly in Stealth Mode, to be the first one who shoots (as it more often than not grants you win). After this first shot, all your Stealth becomes useless.
I just would like to be (at some point) able to "dance in the shadows". With my knife, and nothing else. Leon The Professional-style. Deal damage, and vanish, deal damage and vanish. Put a poison in there, that kind of things.