Best performance mod you'll ever make for the money if you ride in the dark.
A few things you may find of use - that kit is only for one lamp, you can get both for about the same price of you look for car kits - find a seeler who does both H1 and H3 kits and ask them to put one of each in the box, most are more than happy to do this.
There is currently a thread
HERE on Ducatisti where someone has done their 916, it's only one beam but there are pics to give you a good idea. Depending on which bike you have, you may need to mod the switchgear so that both dip & main are on together when high beam is selected if you decide to use a HID high beam.
As for which colour temp, go for either 4300K or 6000K as these are the closest to natural daylight and get the small ballasts as in the item you showed on ebay.
As for 35W vs 55W, I've had the 35W lamps on my ST for about 3 years, the light they produce is superb and are more than enough for my needs.
Go for it, you won't be disappointed.