Is the 55w going to be the best option or are the 35w tipically bright enough? Aso is there anything else i will need to buy other than the HID kit? Like extra wires or the error code eliminator? Also i live in Utah and they seem to be very strict about light coloring, what kelvin rating would you recommend to get the whitest white output?
35w is typically plenty bright. Look at my link in the tech section and judge for yourself from the pics.
http://www.tahoeyukonforum.com/forum/showthread.php?t=6151
I think getting a wiring harness is a good idea, but typically not necessary in these trucks for the headlights. Stock wiring seems to hold up fine from what I've heard. You shouldn't pull any error codes with the headlights, either, so don't bother paying for an eliminator.
If you want the best light output, and to keep the police happy, get 4300K. That is typically the color of all OEM HID's, and is also the brightest (highest lumen rating). 5000 or 6000k are pretty bright and only slightly blue, look good but aren't obnoxious, and you might be able to get away with that.