How many powers does the martian have???

A lot!  I don't even think the writers at DC are sure of his exact powers....

Alot

Basically what Superman has plus telepathy, intangibility, invisibility and a few more obscure ones.

His Martian physiology grants him an almost indefinite amount of control over his body - shape-shifting (rivaling, but not actually greater than Plastic Man's), flight, telepathy, heat vision, super-hearing... the ability to make himself extremely dense (super strength) or completely intangible, and through his shape-shifting he is able to regenerate from nearly any attack. Unlike Superman and the other Kryptonians, his absorption of the yellow sun's radiation does not make him stronger than any other Martian (that wouldn't make any sense), however, interaction with Martian soil - in a total reversal of the Kryptonian effect - restores his body and mind to their proper states. 
 
Also, contrary to popular belief (from other sites, that is) ALL green martians are born with these abilities, including J'onn's brother Ma'alefa'ak, who had his telepathy (and memory) stripped after mind-raping J'onn's wife and killing their mother.