If your going for IJN SS, this guide will show you what sailors you need.
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Sonarman/Planesman use the Potential skill, so roll a high potential (+14/15) sailor for these. Having a decent repair/restore skill on these sailors will also help as a secondary ability. As for Engineers, roll for +11/12 Engine sailors, and +11/12 torpedo for your torpedo sailors.
As for your other questions.
You will need to roll for extra sailors that you do not have. You can do this by clicking "new" on the sailor tab.
Multi-tube torpedo launchers (x2,x3,x4,x5) fire and all their torpedo tubes at the same time, so the reload time given is the time it takes to reload all tubes. As your sailors become better, the time will get shorter. Also, do not confuse Ship torpedo launchers with submarine torpedo launchers, they have their own set of launchers. Submarines have multiple single tube launchers that you can fire gradually by cycling through each one.
All ships have a basic machinegun that fires automatically at planes, however they are not an effective way to shoot down planes. You can also use R/T slot mounted guns to manually fire at planes using AA shells, which is much more effective and helps your sailors gain experts and earn more credits in battle. For all AA guns, there is a certain "golden angle" at which the guns have the best chance of shooting down default altitude planes. However, this can only be done via manual FCS/aiming, which you should eventually get around to learning as its very useful in higher level battleships.
FC ammunition are fireworks/firecrackers. They do no damage and are just there for show.