Are you planning on having servers? If so, you'll need a comfortable buffer such that servers can get to each location without bumping into the people sitting in the next row forward.
Frankly, Movie Tavern (first run) has a pretty good layout for this. Basically, seats are simply high backed office chairs. These are arranged along what is essentially a counter that functions as the "table". When the chairs are up against the counter -- as when someone is seated and eating -- there is a good 2-3 feet of space for the server to wait on the people behind. Each seating location takes up about 3 feet of linear space. It is not a dense pack.
I've been to other theatres that were converted standard auditoriums. They remove two rows between every third, placing a raised counter in the empty space in front of the rows of seats. No servers, so they didn't leave much space between the table and the next row forward. The major drawback to this layout, is that people are going back and forth in front of people -- just like a "normal" theatre -- but with real food, sometime very hot real food. And there's nothing worse than eating from a table that you constantly have to lean back from to let someone through. Oh, and, because you have to have enough room for the patrons to get in their seats, to "sit" at the table, you have to sit on the front of the seat. Ugh.
I'm not sure how you would get 400 seats in any sort of reasonably sized auditorium. I used to work in an 800 seat theatre -- and a commensurately enormous auditorium. I'm guessing we would have only been able to handle 300 people max in any sort of comfortable way using the second scenario, far fewer in the Movie Tavern mode.
-David