2. Firstly, you could've bribed those guys - even though they're counted as hostile, as long as you don't shoot at that specific group of military guys or try to pass them without first bribing them, they won't attack you. Secondly, there's two alternative paths - one to the east over the railway, and one to the west through a tunnel by a dead stalker and electro anomaly.
3. You're probably talking about a bloodsucker. Haha, yeah, those things can kinda pop up right in your face...especially considering they're mostly invisible except for when they're trying to tear your head off.
4. Yeah, money...is rather useless in the game. Stalker suit is most certainly not the best - Duty's tier 2 and tier 3 suits are better; Freedom's tier 2 suit is better; the Scientist tier 2 and tier 3 suits are better; and the Exoskeleton is also better. Stalker suit is tier 2, for the most part. One game, I had over 10 million Rubles because I picked up every single thing I ever found and sold it.

5. I really don't suggest joining sides, except maybe the Scientists. If you join Duty, Freedom will hate you and attack you on sight - just another problem to add to your list. Same with Freedom...though I think if you join Freedom, Bandits, (and maybe Mercenaries?) will be neutral to you, (maybe). If you join the Scientists, everyone, (including the Military), except Bandits and Mercenaries should like you.
6. Sleeping bag doesn't really serve all that much point unless you're trying to go somewhere without being noticed and don't want to wait an hour for night to come, lol. I generally never use it because I'm a bigger supporter of killing everyone and everything, ;o