HID's will these be ok for my car?

They should be fine and the slim balasts will be easier to position than the bricks that came with mine, hence I am having to get a different kit.

Word of warning though, many of these cheap aftermarket kits have a plastic base which may be too thick to be clipped in to the housing properly, (you know, using that thin wire clip used to secure the actual bulb).
Are they 35W or 55W?
 
No, I dont think so really. The 55W are brighter but TBH as you are moving from Halogen, I presume, the 35's will be just fine.
Let us know how you get on and make sure you post some pics.
Good luck