laidback, you can unequip your off-hand weapon during combat to gain Sucker Punch. It does not cost any AP to unequip something, and it only costs 1 AP to re-equip it. So you could think of Sucker Punch as a permanent 2 AP ability where you don't have to pay the full cost in one turn. Then you don't have to choose between the two.
Like Stabbey and VC said, Warfare would be a better investment than the Dual-Wielding ability since Warfare increase ALL physical damage by 5% while Dual-Wielding only increases weapon damage. In other words, Warfare will improve your Necromancer damage skills, while Dual-Wielding won't.
