2.) As far as cutting performance, the slicer will slice better (who would have thunk! ) but the Spanto is no slouch and is certainly a fine cutter. It also retains a bit more thickness towards the tip which could be an important factor to consider if you may need to use it for some light prying. The Spanto is also Rick's sort of "signature" grind in that nobody else really does it (and Rick did it first).
3.) One of the many great things about XM's is that they are modular. You can always change out the scale (and clips, and standoffs) to your tastes. Out of the three you mentioned, I'd go for the translucent green to start. Looks neat in person.
4.) If you prefer a darker knife, I think sandblasted ti would be your best bet. It is the darkest of the three ti finishes offered. Beadblast is a little lighter and stonewashed is the lightest. Bear in mind though that the sand/bead blasted finishes will show wear more easily than the stonewash finish.
Whatever you end up with, I'm sure you will be satisfied with it. The XM series (IMO) are the best modern/tactical style folders out there and are backed by an awesome group of people.
And some pics of course: (3.5" XM-18)