About your powerplant; yes. Your original grade 4 one costs so much penalty in heat. Such a powerplant makes it very hard or simply impossible to use hot weapons like beams, rails etc, makes it hard to boost a lot and simply may make it impossible for some ships to fuel scoop. Vultures main weakness is its powerplant, you have to consider your build around that before going too far into overcharged.
About armor and shield theres a few elemental things to know. Coriolis ship builder offers a lot of this information quiet visibly. First, theres hull hardness and weapon piercing. Long story short, if somethings hull hardness is over (like +25) the piercing value of a weapon that is shooting it, weapon looses damage. This is very noticable when small hardpoints try to hit something hard. Second, resists. For the sake of simplicity lets say that, ship A has 1000hp of shields, zero all resists. Ship B, 500hp, 60% resist to thermal but -50% to kinetic. Shooting it with a laser that shoot for 100dmg per shot, I will need 10 shots to take ship A down, with a multicannon that shoots for 100dmg per shot, I will need 10 shots to take it down. Shooting at ship B with the same laser, I can only deal 40dmg per shot so it will take me 12-13 shots to take that shield, and with the multicannon I can deal 150damage per shot so it will take me little more than 3 shots to take that down. So ship B who seems to have raw 500hp in shield actually has a lot more against thermal attacks but a lot less against kinetic, that is the effective hp. Pretty simplified but should be working like that in concept. Go to the defence tab on your Coriolis screen and see the two bar graphics there showing you damage taken (%) and effective hp for both armor and shields. You will make good sense of it and possibly your question with this approach.