[sblock=Graf] I think you're obsessing about the 15 a bit much.
The difference between a +2 bonus and a +3 will only impact 1 in every d20 rolls you make. So for every 20 attacks you make, you'll hit on one less. I understand the frustration with having lower scores than others, but it shouldn't make a huge difference to Thromb's effectiveness.
Now, as to the suggestions you requested:
You're right about feats. You could help that a bit by switching Dex and Wis in your build, then adding to your Dex at level 4. That would give you a 12 Wis, but you'd be able to take a bunch of new feats once you got your Dex to 13 (including
Raging Storm and
Astral Fire). If you find some good alchemy items for cold or acid, and Chauzu considers them powers,
Burning Blizzard could make sense with the current build.
For first level, I would probably take
Jack of All Trades. We'll likely be making a lot of skill checks to try to escape prison.
Also, since all of your powers are ranged,
Defensive Mobility might save you. I've found that it's much harder for casters to stay out of melee combat in 4E. The bad guys just move around too much.
Alternately, since Aggravating Force and Spike Wire are both weapon powers,
Dwarven Weapon Training might be nice. I love the thought of a dwarven artificer infusing throwing hammers.
Those are just a few thoughts. I think the artificer will be really interesting to play, and seems to be a blend of Leader and Controller. With a cleric and a wizard in the party already, he'll be a great boost to both roles. [/sblock]