It can't control an electronic throttle body unless you use an additional module. There's a couple people that have done that, but I'm personally not too familiar with it.
Other than that, the rx8 engine shouldn't be too bad. I don't know of any done yet, but there are a handful of rx7 engines running VEMS (mine being one of them). You just set it up like a 4 cyl, and there's a table for trailing spark split for the trailing plugs. I haven't set that up yet, but others have.
Using the original instrument panel might prove very difficult. The tach should be no problem, the ECU drives that. Everything else though seems like it might be a real challenge. I don't know first hand though.
