1:- Depends on the area, and depends on the level.
2:- The game prioritises certain areas - if you simply move the sliders around, you'll have enough power for all systems.
3:- Not sure on this one, sorry.
4:- Yes, anything above the green line increases the power by a certain percentage, up to a maximum of 50%. Increasing Shields speeds up their regeneration, NOT their strength.
5:- It increases their damage by 50%, works on all Heavy Weapons.