[Frederf]

I'm pretty sure new submarine commissions are tied to renown somehow. It's either how much renown you have accumulated or how much you have sitting in the bank. Obviously this makes a big difference.

I think realistically decoys are never available but in some versions of the game they should be late, late, late in the war like '45.

Promotions are for breaking through experience limits and getting specializations. During experience upgrades your crew has the chance of gaining special abilities like diving officer or radar expert which I find really useful. Having a bunch of old men CPOs means you aren't cycling the maximum amount of crew through your ranks to get those upgrades.

As for medals, I believe in SH3 they had a effect on fatigue but in SH4 I don't know. I like to wait until I get enough medals for the whole crew before handing any out.

My crew loadout (USS-Gato) is something like:
Rear Torpedo
1: PO1/PO2
2: PO2/PO3
3: PO2/PO3

Propulsion
1: CPO/PO1/S2/S3/S3
2: --/PO1/S2/S3/S3
3: --/PO1/S2/S3/S3

Control Room
1: Lt/PO1/PO3/PO3/S2
2: En/PO1/PO3/PO3/S2
3: --/PO1/PO3/PO3/S2

Conning Tower
1: CPO/PO2
2: PO1/PO2
3: PO1/PO2

Forward Torpedo
1: CPO/PO2
2: PO1/PO2
3: PO1/PO2

Main Deck
1: LtJg/PO1/PO3/S3/S3
2: --/PO2/PO3/S3/S3
3: --/PO3/S1/S3/S3

DCT
CPO/PO2/PO2/PO3/S3

It may not be perfectly historical but I tried to go for the idea of a CO XO and WO as the 3 commissioned officers and CPOs as being the heads of their respective compartments so I have a CPO for torpedoes, engines, control tower, and one for the whole boat and crew. PO1s lead watches other than the CPO's watch with PO2/PO3 taking up the experienced slack. Seamen round out the more menial labor parts of the ship.

I tend to only fill the leadership slot on the first watch so it kicks in only for sure during battlestations.