Damage bonuses add together directly. So, that part at least is straightforward.
Mids calculates all the damage bonuses for you and shows you the final total damage of the power (although the number it displays by default is the total average damage; you have to mouse over the damage to see it broken down into the various hits and probabilities).
You can have up to 5 of any single set bonus, so you can have 5 huge damage bonuses, 5 large, 5 moderate, and 5 small, and benefit from all of them (if you somehow find enough slots for all of that!).
ED is short for Enhancement Diversification. Wiki link: http://paragonwiki.com/wiki/Enhancement_Diversification
Basically, you get diminishing returns on slotting a lot of the same attribute in a single power. These diminishing returns don't get really severe until after you reach 95%. Alpha powers partially bypass ED - at tier 4, 2/3 of the power bypasses ED, which means 30% here. Damage buffs, such as from powers and set bonuses, are not subject to ED at all. Mids makes the attribute turn red once you've reached the most severe level of ED.
Finally, there is the damage cap, which is +400% for a stalker. That's 400% total from enhancements and buffs, but this is generally impractical to reach without outside buffs or lots of red inspirations.
thanks for ur time and info.. another quick question if I slot assassin strike with 4 mako's would 2 invention dmg next to it not be worth it?
Probably wouldn't be worth it, although it depends on which 4 and what levels. If the pre-ED number is much higher than the post-ED number, you can afford to remove some enhancement.
ok.. so if the pre-is much higher..than the post ed... it means im wasting enhancement? what is considered much higher? have patience with me lol.. ty
and when the pre-ed is red.. can u dumb it down a bit.. is red bad?
No, red is not bad. Think of it more like a traffic light - red means "stop enhancing this attribute, you are already at the cap." You WANT your important attributes like damage to be red, but you don't want to keep going far after you reach red.
If you can remove an enhancement and the number stays red, you've probably slotted too much damage.
I ve been toying around with dmg stats on mids, but need some help. I have spent billions on this em/sr stalker trying to make him hit as hard as possible (namely the assissin strike). I have gotten alot of dmg bonuses . my Damage is +35 percent under misc buffs tab and i have the %45 dmg percent incarnate power.. some of my questions are, how does the 35% and 45% stack up? is there a difference?.... is a huge dmg bonus x5 so much better than x4? once i have huge dmg bonus x5 does the large, moderates and small dmg bonus still take effect? example (huge dmg bonus x 5 large x5s moderate dmg X4 and so on.) ok last, but not least.. on mids when u hover the curser on the attack power you see something that looks like ex: 133.32% (pre-ed 185.5%) whats pre ed? and why is it written in red or yellow? is there a cap on damage of a power? I wanna hit as hard as the assissin strike will allow without popping reds. sorry for the long drawn out questions ty