This sounds like quite the interesting project to take on.
For laptops, running multiple monitors really isn't a problem. Most all laptops today have graphics chipsets along with physical wiring and connections to directly connect multiple external monitors. The number of displays which can be run depends on the underlying graphics chipset. For instance, the basic and older nVidia GeForce chipset in one of my HP Pavilion laptops can run just one external display, but the AMD FirePro that powers the newest of the HP EliteBook laptops can run up to four external monitors at once. The difficulty that you will have is finding a way of modifying the wiring (or using some sort of converter) for the external monitor outputs of your laptop to the display input cables of the extra laptop monitors which are often a proprietary ribbon cable of some sort.
Now, when it comes to tablets I really don't know if it's possible to do what you're wanting at least with the current tablet hardware and software available. Most tablets currently do not have graphics chipsets or connections to run external displays. So, the only way of combining the tablet displays into one tablet would have to be through some sort of virtualization environment and software. While I have seen that OnLive has released a Windows 7 desktop environment app for the iPad, this still really doesn't come close to doing what you are wanting to do it seems, where it's combining two tablets into one.
