Most of HID bulbs are 35W. There's a difference between hid bulbs, and regular halogen bulbs with a little xenon gas added to it. With HIDs, you will need additional wiring that should include in the kit. There should also be 2 ballasts, and 2 bulbs. The bulbs will depend on your car and taste. You should not need HIDs for highbeam.
For my car, 97 Honda Accord, the bulb size is 9006. For your car, it might be different. As for temperature, the higher up you go, the less light output you get. Don't be confuse and think with a 12K bulb you will get a lot of light. The temperature with the most light output is 4.1K. The should be pure white. Once you start getting to 6K, it will turn a little blue. I don't recommend you going higher than 6-8K.
Wiring it up should be pretty simple. You might get highbeam every once in a while because HIDs are meant to be on factory projectors made for them, not on regular reflector housings.