For those not familiar with a Firefly ship,
here's some exterior images and a cross-section. For the deckplan,
this has the top and bottom decks and
here's the "middle deck" areas. The crew quarters are below the forward corridor in the upper deck. The catwalks are over the cargo back on the lower deck. The shuttles are accessed from the catwalks. There's some ambiguous spots in those plans--for our game there's five crew cabins and four passenger cabins. Note that the doctor has a one-bed infirmary to work in.