I wouldn't be so concerned about the gas powered vehicles. It was just the car young Kirk was driving, and we all know from the past series and films how much Kirk (and Picard too for that matter) like antiques from the 19th-21st centuries.

Also, we build carriers and submarines on dry land, with all the support structure holding the Enterprise up, it's not so far-fetched to believe they could build the majority of the superstructure on land (where it is cheaper and easier, same reason we do it) and then do the rest of the fitting up in a space dock.