So I added some more badass ranks and then as I look over my wonderful bonuses it dawned me me… how are these bonuses contributing to me? Is it additive or multiplicative?

It varies? I think. Your base stats are 1, where 1 = 100%

If you have 10% to health, your health is now 1 + (1 x .1) = 1.1 This gets really complicated (and very awesome) when you toss in adaptive shields to the formula.

If it were elemental proc chance, we’ll say the gun has a base chance of 30%, boosted by 10% from the badass rank. .3 + (.3 x .1) = .33 or 33%. Obviously, some of these really only work well when boosted by a large amount, or if the base is already large to begin with.

If you plan on playing for a long time and like elemental weapons, it’s worth slowly building it up. If you’re indifferent to them, skip elemental proc chance and elemental damage as you’re just not going to get enough bang for your buck.