I'm on PC and running Paris, so apply whatever may be useful from this info to your scenario.
I've run 4 monitors for about the last 4 years. Currently, 4 x 18" NEC LCDs at 1280 x 1024. Not a problem on Windows, and I suspect it will not be a problem on OSX. OS9 seems to choke a bit on multiple monitors. OSX should be fine, but the challenge will be getting the drivers written by the manufacturers. At this point, I use 2 MAtrox G450 dualheads, though I have also used rather exotic 4 output video cards in the past. PC only, unfortunately for Mac users.
How useful 3 or 4 monitors are depends directly on the app. On Paris all windows open as floats and operate completely independently, so 4 monitors is extremely useful. Logic would be similar. PT a bit less so.
As far as touchscreens. I scoped that out about a year ago. I had a 20" LCD touchscreen working in conjunction with 3 other monitors. Worked as advertised, and I was able to directly move faders, mute, solo, etc on the screen since Paris sports a fairly large and realistic mixer screen with large buttons and faders. I had even gone so far as to design a custom console to accomodate the touchscreen as a worksurface. Very high "Wow" factor.
BUT , the resolution, at least on the touchscreens at that point, was insufficient to really work well for a DAW, even one as realistically emulated onscreen as Paris, which has much larger onscreen controls than PT. Just a little too coarse resolution to be able to move as fast and precisely as I wanted. And 1 out of 10 times hitting the same spot was a near miss on the desired control. Parallax error is unavoidable to some degree. Not quite ready for DAW primetime, IMO.
The Wacom, I don't know. The idea of a stylus is unappealing to me, personally. I estimate we are likely 1-3 years from the touchscreen we would want for a DAW, and ideally the app iteslf would be optimized for touchscreen, with a specific "Fat Channel" mode with appropriate sized graphics.
That's my take on it. No Wacom or touchscreen in my shop yet.
Regards,
Brian T