Here is a very rough list of the enhancements and their costs that I started out with tonight:

Battle engineer: 41
All core 6
All crossbow training/weapon attachment/endless fusilade 11
All rune arm 16
All int 4
Extra action boost2 4
Arcanotechnician: 39
Arcanotechnician 1
All spell crit 8
All int 4
Uncaring master 2
All pet 9
Shocking vulnerability 6
Static shock 3
Lightning sphere 3
Blast rod 3

Some initial thoughts:

I only had time to play around in the Storm Horns for a few minutes, so my opinion may change once I actually try the quests. But my first impression is that I like the SLA's. They are very cheap, spammable AoE dps.

I love the capstone that gives your weapon an implement bonus. With Needle it's 33 to spell power and makes me question the value of the Adamantine Cloak of the Dragon, though I would want to replace the spell focus on it if I got rid of it.

It's nice that arti's no longer have to choose which element to focus on. Now we can use every weapon in the arsenal: force-based spells, lightning SLA's, and Corruption of Nature. I might consider trying to fit in an electric or kinetic spell power item to boost those.

I did not do the LR, but need to in order to fit in the repair and spellcraft skills. Skills will be as follows: max ranks in spot, search, disable, open lock, UMD, concentration, repair, spellcraft, balance, with 21 points extra. I'll probably go with 19 haggle and 1 in tumble, but that's just my personal preference.

For the two destiny feats, I am thinking epic spell power electric, acid, or force at level 26, and either hellball or doubleshot at level 28. I remember reading that the doubleshot chance is lower for repeaters, so I'm leaning towards hellball.

And for the level 27 epic feat I'm considering epic damage reduction or watchful eye. Epic DR is not that significant, but watchful eye is purely convenience. So I think it's a tossup.

Those are my initial thoughts. I will change the OP after I have had more of a chance to experiment and am more certain about the changes. I'd love to hear what others think as well.