Whatever you do, do NOT buy the SS starter pack from the store. All starter packs contain sailors you don't really need and as a result you do not save cash on buying it.

Skeleton crew for beginners:
BO, stats do not matter at all. Remove all the recruits from him and never add them again.
Ideally you nation class him at lvl 12 then lvl him and the rest of the sub crew on an AA-ship/ BB to about SS4 lvl and then class him as BO. SS1 and 2 are about useless in GB, SS3 often are as well. SS4 is where the fun starts.

Torpers: get as high a torpedo stat as you can. Torpedo caps at about 1.1 M TA, after you reach that, keep your torpedomen at that ability lvl by removing recruits. Can save quite a bit of weight that way.

Planesman: Not a good candidate to "ghost"or remove recruits from. As high potential as you can, 10+ repair ( and restore) for non-elite planesman.

Sonarman: can be delay classed or recruits removed, but only if you know exactly what you are doing. For those that don't, get one with high potential and high  repair ( and restore).

While KM is a great SS nation and IJN is also decent, do get a sub in whatever nation you have a BB in. High lvl engineers make a huge difference in how your sub performs.

DO NOT BUY THE SS STARTER PACK....it's useless.

Instead by some elite repairers.

Some players ghost BO, and use EBV (elite, premium, with vets) torpedoman with reduced recruits to save weight. But I prefer using Elite repairers as BO and torpedo man, and delay class torpedo man till lvl 60+. This gives you more repair rate and restore ability (EBVE BO+torpman around 2.5-3 million repair ability total at lvl 120). For RM KM SN US MN it would be a good idea, because you'll finally reach 40 knot speed cap with those extra sailor weight. However for IJN and RN, the weight you saved from BO and torpman may give you 1 extra knot of speed, at a cost of reduced repair rate and restore ability.

For planesman, I also prefer using delayed planesman, which won't significantly lower the air recharge rate.

since everyone is teaching you, i'll go in other perspective, the explanations first, to let you understand and only then choose which way you want to go.

From my experiences Sub'ing in NF is all about speed - to sail as fast as possible, to reload torps as fast as possible, to regain air as fast as possible, to repair as fast as possible.
To achieve that, means you need good base sailor stats in specific fields. 

Torpers should have +12 in torpedo stat and would be great to have +10 or +11 or +12 in repair and restore stats too. Though hero sailors would be best with insane +14 in every stat. Some would say it's an overkill, but when you'll start trimming those torpers down, to save weight = increase your sub's speed, but still remain at tropedo reload cap, they will be really light. Having good restore and repair stats on torpers will also contribute to other important stats on the sub, like faster repair or 900 soft defence cap.

Now why BO should be skeleton:
Since you planned ahead and have crew weight saving in mind (or sub's speed in mind), Bridge Officeer would only effectivelly contribute to repair or restore stats, since guideline lenght is not important or needed for subs.
So it makes no sence in having BO full with recruits, experts or vets. That's why it should be skeleton = should have 0 rookies, 0 experts, 0 vets.
As stated above it should be classed to prefered nation at lvl12 and kept that way untill you reach at least SS4 lvl.

Now Planesman is responsible for how fast you regain/refill air and potential stat is vital for it. But same as torpers it's advisable to have good repair and restore stats. 15 potential with +10 or +11 or +12 stats in repair and restore would be great! But I wouldn't choose hero sailor for it, +14 in repair and restore doesn't outweight only +14 pot stat.

Sonarman gives you vission when you are underwater, that's why Bridge Operator is not important.
Stats should be same as Planesman.

Well and other slots should be filled with engies and reps, best choise for those would be hero sailors. And later you could use them for BB crew.