Don’t think he would were actual spandex; skin tight clothing + fur = ichy (or at least I would think so :/)
Also, from what I can tell, spandex is more of a default then a rule in DC: the Zataras are an example they literally go around in their stage cloths

;
You also have Giantess and grundy, most of batman’s foes, but The Question is the prime anti spandex DC hero; in fact, he is anti DC hero appearance wise twice over, a good few of the spandex wearing supper heroes don’t cover their faces up at all (superman comes to mind) but were a cheesy skin tight out fit to disguise who they are: The Question wares street cloths(suits) and hides every detail of his(or her depending on how far into ‘his’ plot we are talking) face. that said, chip is a not like The Question in mindset or ability; but I figured it was worth noting.
And honestly, have not given his out hit much thought yet :/
[his picture is him in street clothes, I should have it up in a few :3]
That said he is bit flamboyant; so it might be rather flashy (bright blow with orange details likely) with a mantle or some kind of cape; something to flutter about, probably give him a helmet as well (so that his gasmask can be built into it, likely with some kind of circumventer so that he can smell stuff with it on if he has to (he gets high on fumes kind of easy… and cites are full of fumes…)
As for why he is set on a heroic path and not a villainous one is simple: he is (more then) smart enough to know when someone is doing him a favor, and for two years of his life he was basically a charity case of Bruce Wayne after modified and drank the mutagen and wants to payback the debt somehow. (also, when he messed around with his genes he did a real number on his mental growth and stability; his mentality is a bit under developed

; )
[oddly enough, he things Bruce is
really The Green Arrow: why? Because the Green Arrow is blond and has a beard; Bruce has no beard and has dark/black hair making it harder to see who he
really is, also the Green Arrow uses a lot of gadget arrows. And that the greenarrow dues not protect Gotham gives Bruce even more camouflage. Meanwhile, Batman is some kind of ex Special Forces super ninja who is employed by Bruce: why? Batman is unrealistically good at melee while the Green Arrow is ‘only’ above average while preferring to fight at range: what is more likely for a rich boy, using gizmos from afar as a robin hood type character or punching the other guys brains out with his bare hands before vanishing like a freaking ninja?

also, having been in a very limited space for two years, he had a lot of time to theorize about silly things… think Batgirl will get a laugh out of him? XD
Keep in mind, a Superhuman level intellect thinking at a speed of 32 times faster than one should be able to, that has little better to do then daydream and ponder about super heroes while seeing Bruce Wayne as the man who saved his life and thus a bit of a fixation on him; for two years (or the equivalent of 64 years) and that Batman gets Bruce’s wards as sidekicks and that robin was highly acrobatic while Richard was part of an aerialist act only further conformed his belief that Bruce is the Green Arrow (Bruce is obviously smart enough to let them learn under the Super Ninja guy before they go of an their own ;3)
(hmm, he is acting a bit like The Question here… he might have been acting runner for mister Q; he might have even gotten teamed up with the sluth to become a bit more perceptive while making the suit loosen up.

; )
-End pointless side tracking]
Also, he has a generally good and helpful demeanor so he is not likely to consciously turn bad any time soon. That said he might in the future; who knows :3
(his mindset could get warped by a tainted treatment as well, he has alot of room to be a switch hitter acutely :3)
As for why is chose to be a side kick first and not just go off on his own; he is a bit of a kid still, and working with real super heroes while learning from them? He is more than smart enough to see the opportunity here (and that being around others who know about his condition and have recourses to get him treated as sap if his condition suddenly changes is a good thing) while also being a bit giddy about working with people who should be in comics/cartoons (another thing, he still reads/watches them, if a TV ever factors into things and it is just being used for casual viewing, expect Bugs Bunny!)
Anyways, his outfit might end up rather militant with some Batmanish inspirations; a sketch I did with a ‘dramatic’ cape just looks to strong and imposing for him. Then again, I might make him a “looks imposing until he talks” character XD
So, I think I will post up the aborted draft of his ‘hero’ get up when I post up his appearance :3