Well, not really. Your volume cannot change. You could make yourself look larger by making parts of your body empty. But on the bright side, depending on how the control works, you could summon thousands of needles and then launch them at your enemies, since you don't need the metal to be connected, you merely need it to be close enough so that you have enough willpower to control it. And you are also limited by the size of your braincase (unless you get that genemod that spreads your brain and a custom flexible braincase) so you can't fit through everything. And you need at least some mechanical limbs to take care of movement so that you don't have to expend willpower every time you want to move or make your body look like it's moving. And said limbs should be capable of fine manipulation if you also want them to take care of things like facial expressions, so parts of them at least would be very fragile. And there's also the problem that if you want to make bodies look and feel right, then you need to be able to make weak malleable parts of metal which will be able to bend like skin does, which means even more fragility.
Overall, a T-X sounds like a choice more suited for a combat character with some space magic and charisma/stealth capabilities. The other choice is more for a quick moving, sneaky, stealthy, space magicky glass cannon... which is partially what your character is, although you probably lack the dexterity and charisma to properly utilise it.
EDIT: Unless you can get away with using a proxy brain for it doing the calculations for the skin and movement, but then you just switched the problem of your brain exploding with the problem of the proxy brain exploding. Which means that thing is going to burn fuel (read "brain batteries") fast.