If you need a visual for what the ship looks like, think something kinda like the Katariah from Skyrim. It has the above decks level, which I suppose counts the captain's cabin, since that is raised above. Beneath, it has an upper deck and a lower deck. In this case, though, it doesn't have all the luxuries of that ship. After all, this isn't the emperor's ship, so the interior design is different. 

As for the demographics of the NPC crew members, they would match the demographics of Leyawiin. The city has a high population of Argonians and Khajiit, as well as Imperials, so they would be common races, with a mix of others as well.