What determines the amount of damage that a armor plating I've attached to my bot can take?
I am guessing that the material type determines bullet deflection, but what determines the hitpoints?
Also, where does it define how much damage is taken from collisions? I see in someone else's mod that their actors can be dropped from map ceiling and hit the ground without damage, whereas my actors disintergrate on impact.

Found the one of the answers by looking at the DSTech mod, the structural intergrity line defines the HP of an attachable.

...huh? The structural integrity is more like the "defense," if we want to go by RPG standards. GibWoundLimit is more like HP. And one is lost for every hit. So, if you want your armor to take 10 hits, give it a GibWoundLimit of 10.

Higher structural integrity will cause the armor to resist penetration by projectiles more. The higher it is, the faster, sharper, and heavier a bullet has to be in order to penetrate it. Of course, it also determines whether or not a round goes all the way through and causes an exit wound as well.

Now I believe there is also some variable that determines how much TOTAL blunt trauma something can take over time before it just gibs. I think its GibImpulseLimitPerDensity or something like that, in the material code. I can't remember the exact name of the variable.

I originally though gibWoundLimit was how many sprites of wounds the component could display at one time. Thanks.

what would be a good structural intergrity value for stopping light bullets? but not heavier ones?

Check the Base.rte ini's, they have decent learning materials.