Cree LED questions

Well to start out the tank I am going to build a LED fixture for a 30g aquarium which is 36"x12"x16". I want to keep LPS, zoanthids, and clams; and eventually move up to SPS corals.

I want to use the Cree XM-L LEDs but I don't know how many I can safely put over a 30g aquarium without killing off coral.
Which drivers would work with XM-Ls as well as be dimable and affordable?
What color ratio would work best using XM-Ls and RB?
And my final question is should I use a row of LEDs in a line or make 3 LED pucks on a 4.25" x 23" heatsink.

Why do you specifically want to use the XM-L? Honestly, for a tank of your size, it's not necessary. It's not like you are going to use fewer LEDs when compared to XP-Gs. An XP-G and XP-E setup will do everything you want, and more, and cost less than the XM-L setup.

If you want to go with a traditional grid style setup, you can easily light that tank with 24 LEDs in a 12x2 setup. That will keep everything and anything you could possibly want when driven up to 1000mA. I advise getting dimmable drivers so you can easily set the color temperature, and the overall intensity to suit the needs of the tank.

Ok thanks for the reply I just ordered the XP series of cree leds. I ordered a 2:1 mix of RB to NW and was wondering if staggering them like this would work.
RB,RB,NW,RB,RB,NW,RB,RB,NW,RB,RB,NW
NW,RB,RB,NW,RB,RB,NW,RB,RB,NW,RB,RB

Or would a 3 led cluster w/ 80* optics work, and if I were to go with option 2 what would be the best distance to space the clusters from each other.

Either way will work, but you shouldn't need to use optics unless you are mounting them somewhat high over the tank.

If you cluster the LEDs, spacing of 3-4" should work fine.