WEIGHT is the biggest issue you will have to deal with.  If your BO is heavily vetted you will pay a price for that. 

You can get a pretty decent sonarman around level 50.  The planesman is where you need to spend your credits if you have them.  Planesman gets workable at 90+.  I think Torpedo reload caps in the 50's but I am not sure on that one.

If you have 90 or so engy you should have success but SS is high risk high reward and everone that is NOT a SS hates your guts and are looking to eliminate you from the game as quickly as possible.

Hopefully you have 2 BO resets in case you change your mind.

Hopefully not more than 10 levels behind your ship level. At that point you are already earning only 88% of the total possible exp that sailor can gain. The perfect would be no less than 4 levels behind your ship lvl.

After that big issue, your main concern will be if torps will be able to be used. That will depend entirely on the nationality as each torp launcher requires a different level, but all of them are close to the lvl required to access the SS. 

Sonarman: at level its OK (from SS3 and after)  but look for a Pot elite or +15, BVE... u have to take it on support slot all the time. Better s.onnar = seing your enemy SS before = the advantage

Planesman: at level is decent (like sonar you should pick Elite pot or +15 and BVE it). again, put him on support. Better planes = fast reload of air = less time on surface = advantage

Torps: at level of the torps your SS carryes are OK. if your nation uses 2 torps only waste a boost on the front one, with 109 vets and full exp should be OK. the rear torp its not important, so leave him with something like 50 to 100 vets and anything more (you don't need much of reload on your back torps and you really need the space)

Engy: how much depends on SS, but for a KM SS4 you need 1... AT VERY HIGH LVL. Elite its almost a must, but can also use a +12 with good base on rep and rest. BOOST AND OVERVET is also a must.

BO: no matter the stat at potential, just search for good stat at rest. you have to put something like 40 to 80 vets and nothing more

I don't think he's asking what level the sailors should be for performance.  He seems to want clarification to sailors needing to be at least the level of the sub to work.  If I remember, this was an issue for some people when they had lower level torpers with matching abilities but their levels were below that of the sub.  Unlike other ships where you can only purchase weapons when you have qualifying sailors, subs come pre-equipped so it can be an issue.  I'm not sure about planes/sonar but for torpers, you could check the component list on this website to see exactly what level the equipment is.  Generally I think ss1 and 2 use the same level launchers, then ss3 and 4, and finally ss5 has it's own launcher.

Thanks for the input guys!  what minimum level that will operate my torps is the main concern, but I definitely appreciate the performance tips!

I didn't quite know what I was doing when I 1st started Navyfield years ago and I have several crappy BO's  on an older account.  I have a few that are high lvl that I don't use and I got a BO reset for a prize some time ago.

Torps are shared between T1 & T2 subs, T3 & T4 subs, and T5 subs are their own. As such, the subs must be at the level of the tier they are shared with. (T2 can use T1, T4 can use T3 level)

It varies by nation but a general rule is you want torps to be around 50 for SS1/2 and then there's a jump. The tubes (like the guns on a surface ship)for torps are 59+ for SS3/4  Sonar and Planes aren't tied to any tier so a lvl 20 sonar will work but not very well. same with a low lvl Planes.  Just like any other support sailor, the higher the ability the better the performance. sonar caps but Planes doesn't or so I'm told.