I'll second jimmejames' suggestion to start at the wiki. Just to expand a bit:
Instead of trying to get a converter box or a new TV, pick up an older nvidia card with s-video/composit output for each MD. Check the wiki for supported cards, but as an example I have a NIB sub $50 nvidia 7300 on my core/md and it works great. I'd bet you could find plenty capable cards on e-bay for dirt cheap.
Last I read, the PS3 is not supported. Lots of technical issues.
wifi is basically a no-go. wifi cards do not support pxe boot (network boot), and this is required. You may be able to hardwire a computer to a WAP and get it to boot, but that's beyond the scope of LMCE. ie - your on your own but others may be interested.
usb webcam - as I understand it, yes, this works.
tv tuners - I'll add to jimmejames' post by warning that some cable companies, mine included, are switching to digital (QAM). Do some research into what tv cards are supported by lmce as well as which work with your cable company.
game consoles - your best hope for this is to capture the video out from the game console via tv-tuner card and treat it like any other A/V equipment and transmit it to another MD. However, unless I'm wrong LMCE does NOT pass on bluetooth signals so you'll have to be close enough for the controller signal to reach the console directly. You are also going to see some kind of delay which will likely make games unplayable.