Not sure the engines on Serenity are jump drives. Actually not at all sure how they are supposed to work, but I get the impression it would operate more like stutterwarp than jump drive. Other than that, either 2300 or CT or even T20, the show screams for a RPG conversion.
I figure the shuttles are about 10 to 15 dtons each. The cargo bay is kinda tough to figure, been wearing out my tapes trying to work it out. So far I have 5 cow widths wide and 18 paces long, at the bottom, 3 or 4 levels tall. This is just the cargo bay.
There is a movie being planned, and apparently all the cast has been signed to start shooting early next year. The only clue that Joss has released as to plot is "Reavers".