Before you start on such a project, I wonder how many people can a 110" screen accommodate for 3D.
From my testing, the 3D picture falls apart very quickly when viewed from outside the screen area. Having people on the side of the picture is in my opinion not suitable at all.
Same problem with using high gain screens, which usually have narrow view angles.
If also you intend to use this setup for a party (sports/movie/game/...) with people scattered around the room, you might reconsider (both the scope of the 3D project and the high gain screen)
I just can't imagine 25 people watching 3D simultaneously in front of such a small screen, unless you pack people tight like sardines and have multiple rows of seats.
If you're still going for it, then I'd recommend a passive setup, dual-projectors is a bit complicated but it's what gives the best picture, gives a great design flexibility and isn't that expensive (considering you are aiming for 25 people).
I have been using a polarised dual projectors system for 1,5 year, and it's my current benchmark but the silver-screen requirement (high gain, small viewing angle, a significant amount of visible grain structure, and very fragile). I am testing the Omega filter system at the moment, and Omega is winning my heart. There's just one annoying thing with the Omega system : it has youth issues. The filter kit is still kind of a "beta" program. As more people test them, we discover issues with certain types of projectors. My Epson LCD projectors for example have colour problems due to the light spectrum being outputted (3-LCD projectors with UHE/UHP lamp) being different from the reference projectors the filters were designed for (DLP projectors with Xenon lamp).
The guys at Omega are quite reactive though and are working an a modified filter which would be better suited for LCD projectors, however I am sceptical and am waiting to see the updated filters before acknowledging the Omega system as a good consumer choice. (and they have to provide other glasses than their current "theme park" glasses design, if they want to succeed in the home, because they're REALLY dorky)
If you would like to learn more about the Omega filters, you should head to the "ultimate 3D projection" thread http://www.avsforum.com/avs-vb/showthread.php?t=1280393
Where current users share their findings and an Omega Optical employee reads our feed back and answers questions.
Regarding your other questions :
1 - 2 - 3 ) I don't know I'm not up to date with those.
4) The Omega kit can currently only be bought on ebay, you can find a link on Omega's video presentation http://www.youtube.com/watch?v=6ziuTZQx7dg
5) You'll need two separate inputs, and both should support 1080p if you want to get the best of your projectors. A single VGA link won't be enough. Also you should know that 3D is filled with copy protection systems which usually mandate Hdmi transmission.
I haven't tested wireless Hdmi devices, but I'd rather stick with proper cables.
Also the number of cables or wireless transmitters will depend on what type of source you want to use.
6) There are two options :
-A computer with a suitable graphics card and lots of software (and a BluRay drive if you want to watch BluRay 3D discs) = 2 cables all the way from the computer to the projectors
-An Hdmi 1.4 3D source (BluRay 3D player, PlayStation 3, etc...) with a series of converters to split the single 3D Hdmi 1.4 stream into two two usual Hdmi1.3 video streams running in separate cables. Typically one Hdmi 1.4 compatible splitter/cloning device and two Optoma 3DXL converters. = 1 cable from the source to the splitter + 2 cables from splitter to converters + 2 cables from converters to projectors (not including power supply)
The computer is the most flexible system and can reach resolution and framerates higher than anything else (it's the only way to do games at 1080p+60Hz), but it's very complicated to get everything running (very few of the easy "3D" ready software supports dual-projectors, you have to hack most things to make it work).
If you're not interested in PC games, I recommend you go for the other route.