If your going for IJN SS, this guide will show you what sailors you need.

http://navyfield.com/Community/Forum/View.aspx?num=6273&searchtype=0&pagecount=0&searchvalue=&sort=5&category=A03&page1=1

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.

Thanks for your reply.

Very helpful!

I also found some old guides on other pages.

Will learn how to aim manually once I got a hold of everything else.

A few things made me wonder today even after I read all this...
Should I max out crew size in the beginning? Seems to make my DD quite slow.
Same for the use of armor...

Wouldn't I be more successful with as less weight as possible and torpedos?

And what is the use of xtra ammunition for main  guns on small ships (I never run out of it due to a combination of low range and low armor)

Well what i did is, i got a lot of generous friends so try to get torpers that are 10 levels above your BO so you donthave to worry about your torpers lagging behind. Try to get every sailor 10 lvls above your BO because i started out with full air when i got my ijn ss1. ut what i noticed to be easier was i got a dhonburi with the olive attendance and lvl in that. You have a higher constant exp gain when you do this. Also if you will need 3 engies for ss5 2 reps, and etc. This setup will make your grind to the ss2 and ss5 much better.

Thanks for all your advise.

Unfortunately I don't have any generous friends, so I'll have to train myself I am afraid.

Still following a steep learning curve and wonder whether starting out with subs is the best thing to do.

Also what happens once the BO has reached a dead end (Kitakami...)
Do I need to train an extra BO? Or should I trade one?

Don't want to start a new thread because I am a beginner as well and am ranking for an IJN sub also.  

With support sailors: is it wise to use KM crew for Eng, Repair, Planes and Sonar?  I started KM and am working IJN and I'm wondering how many of those guys can cross over effectively or should I roll for new IJN guys?

KM sailors will work on IJN ships HOWEVER they will recieve penalties to their effectiveness.
Those penalties are severe and you really should raise IJN sailors instead of using KM.