A fun idea. A few things:
Art of Silent Death - This skill (originally from Skaven) has pretty much become synonymous in Mordheim with Martial Arts. It grants the attacker unarmed attacks plus extra chance of critical hit. I'd either use it or something based off of it, as it will make him feel more tied into other kung fu models.
Robes - HE can call them robes, and they can have the same effect, but I think you need to poke fun at them. (Ex. "made from a thrown away silk hanky")
Magic - The idea of snots mimicking kung-fu kicks and such make SOME sense... the magic thing makes slightly less sense. The concept seems silly and comical- and then the execution seems dead serious. I suggestion you approach some of the special abilities / skills/ fluff from one of a few different ways:
snot it up: I'm not one for gross-out humor, but if it's Snot Fu, where's the Snot? That could be the source of his power- the ability to throw disgusting things at people, to the point that they wretch and dive for cover. (No effect on models that are immune to psych, of course.) "Burning Fist" could become "Flaming Bag of Unmentionable Content".
Waagh Magic : he could use a form of hth magic... if so, make it more Greenskin. Have it gain bonuses from nearby greenskins. Have it backfire. Instead of a Burning Fist, maybe it's a giant foot. Look at Orc and Goblin magic tables for inspiration.
LOOKS like Magic : what if "Burning Fist" was really a flaming bag full of gunpowder? to the silly snot, he THINKS he's pulling off kung fu magic moves... when really he's just throwing dangerous things around.
In general, Greenskins (especially Gobbos, and x2 with snotlings) are defined by three characteristics:
1. A dark comedy aspect (there's humor, though most of it is derived by pain.)
2. Inflated Egos - They are confident of their strength and self worth. Also, to a greenskin, everything they conceive is "brill!" They paint their meks red, ('cause they're skientiffacly proven to go faster), they have constant headbutting matches over top dog. They are vain at best, and delusional at their worst.
3. Randomness. Greenskins are all about "they're stronger than everyone else... but they don't work out like you expect them too.") Squigs hop about like crazy, trolls are stupid, henchmen squabble.
this list could use a little more of all three.