Fearsome

Fire hands down. Most AoE damage I have seen, although you have to stay alive long enough to use all of it .

I would take CJ and start your travel.

I would not take repulse, nrg prot would be a great place to put a +3% def IO.

Since you are new to MM I would push you towards Bots, the undead take quite a bit of micromanaging in order to take full advantage of them. Bots are probably the most self-sufficient MM pets and dish out the damage on insane lvls, granted it wont seem this way till post 26 and more so post 32.

My recommendation:
Bots/Dark - Could fit theme of having Tech pets and dark witch powers. This is a very powerful combination. Once you get your lv 32 upgrade the Assault Bot gets Hellfire missile with that stacked on top of your Tar Patch its a thing of beauty.

Second the defensive set of metal or metal adding armor for each different armor. More of a modern tech armor, with the tier 9 being like granite where it is a toggle but very heavy.

Growth/SS FTW!!!!!
I dont agree with having some of the growth powers shrinking the hero, its growth you dont grow shorter!! Who cares about not being able to see part of your toon in caves, we all hate cave anyways, but they will see your massive foot coming down on thier heads. I might be alone in the aspect of wanting to have all of the powers increase the size of the hero but I would love to be so big that it turns everyone else into anklebitters.