I've never played MK before on a stick and was wondering what I should map the moves to. I have one of those Street Fighter 4 sticks, should I just stay on default?

If you have eight buttons I'd map the four in the middle to the punch and kick buttons, and have the four on the outside to all be block for easy access.

You also need a tag button and an L2 or LT for X-Rays

If you have a Mad Catz TE you can get this panel for it:  http://shoryuken.com/content/completed-mad-catz-combat-fight-stick-panel-pictures-3837/

For reference, this is what the fight stick that comes with the tournament edition of the game looks like. Pretty much the same layout every MK cabinet has as well.
 
I'm honestly not really sure what the best way to map that over to a SF style layout would be. Personally, I'm half-way considering that it might be better to just use a standard controller (...but damn is that 360 d-pad terrible for fighting games...)

I would probably map the buttons to LK (bottom left) as block, LP as tag, MP and HP as left and right punch, and MK and HK as left and right kick. Of course this is all in reference to the Street Fighter layout starting with the far left buttons.