Hi,
Well as far as answering your question specifically, we are not a consulting firm (I can be, but I’d have to charge you for it 😀 ).
We can give you some advice, pointers and such, but you have to do your own homework too.
You are making the switch at the right time. Digital DJ software has come of age and many programs have great integration with Video. VDJ and Cross for example. Take a look at their websites to see how they implemented video in their workflow.
If I were to go video, I’d get one or two powerful projectors. Not sure I’d go and set up screens, as they usually look cheesy or are a bitch to set-up (like a tight screen in a truss frame). I think I’d try to use a big wall or (slanted) ceiling or whatever else is there.
Another option is to have the beamer project from the back on the inside of your DJ booth (which needs to have like a semi-seethrough front of course).
I’d use Cross (which is my preferred software at the moment anyway) and just click on the video button, hook up the projector(s) and go for it. No need for anything extra by way of soundcards  or such.
Greetinx.
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