Keep your BO ghosted no matter what no rookies no experts no vets, you will need the weight for other sailors.
I would also skip the SS1 and 2  ( you can't really use them for offense) and only think about classing him for SS3, but going straight to 4 is even better.

Planesman 14+ potential and good repair, class him on time, but try get 15 pot. A planesman needs to have 90% of its crew filled or you'll start the game with an empty airtank.

Sonarman 14+ potential and good repair. You can delay class him, but you really have to know what you are doing AND planning on putting (way) more than 100 veterans on him.

Engineer, as a starter I wouldn't delay class them. On KM SS5 I'd go 3engineer and 1 rep for GB.

Torpedoman, you can delay class them to gain some repair rate but the gains in repair rate aren't spectacular. Plus you end up with far heavier torpedoman. I'd go with the best torpedo stat you can get ( with good repair), class on time and trim rookies to keep the torpedoman just above the Torpedo ability cap. Ghosted BO and light torpedoman allow you the use of the heavy planesman/sonar/engineers.

1. Late classing of SS BO benefit you that you can lvl that sailor with other BO example bb BO
No recruits(rokie,experts,vets) 
2.Sonar&Plansman you can delay class up untill you get 1st ss
Engins,repair and torpmans class on time 
3.BO - 0recruits
trim sonar and torpmans whean they reach cap
Engines,plans and rep keap alwayes full of recruits

You can use your BB crew ofcourse

For km ss line you will nead this crew
BO
2xTorpman
Plansman
Sonar
Repair
4xEngines

You can PM me if you have more questions

A couple of varibles to consider:

Up through the SS4, the KM subs only have 3 supports for which you will use two of them as Sonar and Planesmen.  The only available slots will be the last remaining support slot and possibly replace the gunner with another support sailor being upleveled (if you don't want to use the pop gun).  

The SS4 (U-Flak) uses two gunners. You can skip the gunners and put on your engineers and repairman to uplevel, or put two lightweight gunners (L77) that run one of the best AA/HE combo guns in all of Navyfield.

When you get to the SS5 (Type IX) you have 5 supports and one gunner.  Your second gunner is now useless and when you get to the Type XXI, your last gunner will also become useless, along with your second torpedoman.

There are 7 Support slots on the Type XXI (Sonar, Planesman, and any mix of engineers and repairmen), preferably 5 Boosted Elite KM Chief Engineers, but you probably won't have that many ready to go by then.

So consider the final stage, but try to enjoy what they offer at each level.

 

           

I was told that the TA of potential of the BO determine the range you detect enemy torps, is that so?