I just got a legendary 10mm pistol that does 10 extra energy damage per shot. I'm wondering if that 10 can benefit from my stealth perks that give me 5.3x bonus damage, or if it will stay a 10. (and by extension if it works on any damage perk like gunslinger, bloody mess, lone wanderer - you get the picture)

I'm also wondering if all the other legendary effects do too (for example, the bleeding effect or the explosive effect). I'm guessing that the double damage when target has full health does, since it's a multiplier, but not sure about raw damage bonuses.

They stack, but there are a few exeptions. Double damage at full health + Critical Damage. Better Critical L. Weapon + Better Critical Perk. There MAY be more exeptions but this is all i know