I would say that it definitely is still a viable option now. There are way more options in terms of multitouch software (Windows and Android come to mind) than there were and hardware is cheaper as well. I just got back to working on my own table that will eventually have a similar role that you were aiming for. It seems that unfortunately the more common availability of touch device in a smaller form factor made building large tables less novel, which may be way things are a bit slow around here. But I still think for a social situation, they can be used in really interesting ways.
Anyway, about your questions:
1. The Raspberry Pi is probably useable in theory, but the software (CCV 1.5 or alternative) you need would probably slow it to a crawl… and thats assuming you can even compile it to run on an ARM processor. Performance is really key here so I wouldn’t go down this road. I would definitely look at running this on a desktop for optimal performance or a laptop/compact pc to save on space.
2. The PS3 Eyes are still pretty handy. For the price and performance, its hard to beat them still. That said, webcams probably have gotten better in the last few years, but these are pretty solid. The eyes and the parts you need to mod them can all be found pretty cheaply online. My online complaint here is some driver problems that haven’t been resolved since Windows 8.1 came out. You mentioned OSX so you might not have any problems, but I cant really confirm that one.
3. Fiducials. My table is about the same height, which is really pretty low. I had 2 PS3 eyes with really wide lenses on them(2.1mm) and had some problems due to heavy image distortion. I ended up adding 2 more so that I could use lenses with less distortion. In short, you will need at least 2, maybe 4, but definitely not 1.
4&5: I haven’t ever used a projector so I can’t help here. I’m using a fairly cheap LCD and its turned out pretty well. If you decided to go down the LCD route, there are some things you need to be aware of. Fiducials are really hard to get working. This is because of the diffuse material being so far for the touch plane which blurs them out. You could reduce the diffuse layer, but then you will see through the screen to the inside of the table. Also, Rear DI will not work with nearly all LCD panels because they reflect the IR back down. Look up LCD DSI if you choose to use the TV.
6. The software really depends on your platform. You will need a Tracker, a driver to convert the tracked points to the platforms native touch points and then actual software to interact with. Community Core Vision (CCV) is the most common tracker software that you will see around here. Reactivision is another popular choice. Neither will run on a Raspberry Pi unless you do some serious leg work and the performance is guaranteed to be less than amazing. The trackers are pretty intensive. Personally, I’m using Windows 8.1 here because it allowed me to build an affordable and modular PC that I could build into the table and also have access to all of the touch enabled apps that are in the store.
7. Anything can really be used to create your apps. The Trackers communicate using TUIO, which the drivers convert to touch or mouse points. You can skip that entirely and just use the TUIO output to interact with your app. A lot of people did and still do this and I think it might be necessary if you are going to use fiducials. I remember that many apps were written in actionscript so you might be able to dig up plenty of examples I sure.
I hope this helps somewhat. I haven’t really played around with OSX so your experience might be different on the software front, but hardware should be similar. I learned a lot by trial and error and redoing work over the last couple years but its also been pretty fun and I’m still pretty excited for it to be done and in use. Good Luck!!