looking for some constructive criticism on an image i am working on

i am new to photoshop (downloaded the trial last night)

i decided to edit a picture of maya i liked.
i started with this



added my favorite maya head, changed some hair color and so far i have this.



im thinking of making this into a sig. i was wondering of what you guys might think is a good background for it, and what should i change the size to?

and of course how do you think it looks so far? do you think i have the right lighting for the head to work with the rest of body? what do you think i should change? im also thinking of trying to change the gun she is holding later on but that might be too difficult for me to handle.