The first choice to make in planning a vessel is to determine if it needs to operate in atmospheric conditions, or even if it might expect to do so. This will determine whether rear-facing engines are required, but STL engines will also require this. We should also decide what sort of ship it is (cargo, war, passenger), as this determines the amount and type of quarters, and dining or entertainment possibilities for crew. Next we should decide how passengers and crew typically board or exit the vessel, where they stay, and what they do onboard. We can also determine the purpose of our ship, such as travel within a solar system or between stars. This will help determine what sort of additional engines it has. Lastly, we should decide the events we’re intending to take place on this vessel so that we can decide what sorts of vulnerabilities it might provide us with and how characters and story might benefit from these; but we can also start with this subject. The best choice is to go with the subject that gives you ideas first, then return to less inspiring areas later.