I've just started an Iron man account and I thought it was time to learn Full Manual while I was at it. However, I'm still confused of some elements of EOC whether I'm getting the most DPS out of it. These question are the following:

Do auto attacks in between abilities improve the DPS (or perhaps only for fastest weapons)?
Does attack speed scale with abilities?
Does an off-hand improve ability damage, or does it only provide additional abilities?

Thanks ^^

I'm not sure about the first, but abilities generally deal the same damage with the same tier weapon. One change cancels out another. An offhand weapon adds to your base damage, so it is indeed additional damage compared to just a main hand. The base damage is the same for main hand + offhand as 2h though (barring the access to different abilities).