Having a skeleton BO is a must, potential doesnt help sub vision range and it will only slow you down to run a full BO.
Torpedo ability caps fairly quickly, so with enough vets/exps you can trim off your recruits without it having a negative impact on torpedo reload. Its not essential at low levels but it is advisible at higher levels.
Most SS guns are just a novelty so having a gunner onboard isnt worthwhile, you can save weight/gain speed with gun slots empty or put a Rep/Restore sailor in them for boosted support abilities.
As for supports, do not skin them down. Sonar, Planesman and Engine are all extremely important abilities for SSs.