Okay so I got the pics, couldn't find the yard stick to measure but its from TSC
Ok so that's about 4x6... you said you have 7 chickens? I'd consider turning this entire unit into a coop once you have the larger run built. Even with some bantams the coop on this really isn't big enough for 7 once they're all adults.
As far as the deep litter, that might be tricky with a small run footprint as it can only absorb and compost so much at a time plus it can get thick (in fall, with the leaves, mine gets 4-6" deep before it starts breaking down). Doesn't hurt to try it out, but don't be disappointed if it needs some maintenance vs how it would behave in a bigger run.