You need to do a full breakdown plan of AC, not just dex and armor. If you're not hitting 50/55+ at endgame, you might as well just have 20 AC for all the good it will do you. On a build like this with a lot of feats, your motivation for 15 starting dex should be to hit 17 with a +2 tome and qualify for the TWF feat chain.
Your best DPS-increasing feats are:
TWF, ITWF, GTWF, and most importantly Power Attack, regardless of race.
One of the other important things to note is that any battlemage build is
VERY gear intensive. The time you invest grinding raid gear and building wealth for the expensive items will matter more as much as what feats you take and your stat distribution.
For what it's worth, my main toon is a Battle Mage. He's on myddo
here. His gear is the most expensive of any of my characters and he's ground out more raids than any of my characters. You just need to be prepared to do some serious investing in a battlemage build for it to work AT ALL (IMO).