Im sure this is already on here somewhere but I cant find it. How do you aquire psyker powers, do you just pay the listed points cost or have to list a talent to take? Also, is there a limit to how many powers you can have? Or is it possible to spend all points on new powers every game?

you just buy the talent for the proper cost, you can buy it as often as you like but your going to find yourself very lacking in all other areas if you focus that heavily on your powers, you will also be very sad if you roll any perils results that deny your use of powers for some odd amount of time.

Exactly. There may well be psyker concepts that work very well only focusing on powers (chaos psykers utterly devoted to their powers and disdainful of the Materium), but most of the time, a more varied approach will yield better results.