Q: How does he keep his hair so greasy?
A: If he's the potions master, he must be the cleanest of the school. Brewing potions need clean brewers, no? Maybe his hair is just greasy because he washes his hair too much (it could happen) and not because he doesn't wash it at all. So the answer to your question is: I dunno.
Q: Was his nose always that hooked?
A: No. He once walked into a wall as a child.
Q: Will Snape ever braid his hair?
A: No idea. I have heard rumours, though.
Q: Are all these answers true?
A: Probably not.