Kckolbe summed them up recently.
Captain: Braxton T. Early, former wealthy rancher, militia man and current slave owner, owns Elfi
First Mate: Richard Dawson, backwater aristocracy and former militia
Engineer: Lance Daniels, former Alliance enlisted, silent partner in business with Braxton
Pilot: Keridwyn "Keri" Jones, outer rim commercial pilot
Medic: Mya Richone, rich kid from Osiris, now indentured servant
Grunt 1: Girias "Cookie" Bomban, ex-con, rural background
Grunt 2: Sue, former ranch hand and tinkerer, ship's cook (backup mechanic)
Other: Philemon "Phil" Adricus, ex-Alliance infantry and ex, abolitionist
Ship Slave: Elfi, owned by Braxton, from a mining colony
Companion: Serenity Sun Kwan, opposed to slavery
But don't feel limited to what you have seen in Firefly. Anyone who has a plausible reason to be on board is welcome. Post your character proposal and we will discuss it.