you can go many ways... if you go with bi-xenon projectors, you can still use the halogen highs with the xenons... you'd just have amazing high beams. If you want normal xenon projectors (generally cheaper) and still projectors for the high beam, there are certain high beam specific halogen projectors... that produce the proper beam for high beams. 4 of the same projectors wouldnt work out right, as you'd end up with no high beams really.

And YES you do want high beams with HID. HID projectors have such a defined cutoff line that the road is all nicely lit up, but nothing above... if you ever left the city you'd really wish you had left your high beams on the car.

Search on ebay for HID projector, Xenon projector or D2S projector... you'll find all sorts of goodies!