[Maz]

1) What do you mean by "temporary"? If you want, you can create new techniques, using all of the rules. "-1 per die" is just one way to modify a technique.


2) Instead of seeing techniques as "allowing something new" see them as "buying off penalties to do one specific maneuver". So yes, it is not cost effective to buy many techniques for one skill. Techniques are for when you want your character to be really good at something very specific.
Also be aware that some techniques are much more generally good than others. As you are going to use them very often. Stuff like Targeted Attack or Feint for instance, compared to maybe Choke Hold.
Techniques are a way to specialise.

3) you could use the rules from MA p.104, although they are mostly for opposed fast-draw rolls. I think Tactical Shooting, Action or Gun-Fu have rules for position of the weapon (belt, pocket, ankle and so on) (sorry I don't remember which).

4) Yes. GURPS is designed so defenses are lower than attacks. At high skill levels though, those defenses are still going to feel really high. Remember you can get bonuses to your defense from stuff like Retreat, Shields/Cloaks, Acrobatics or, if suing those rules; Extra Effort.