The IJN SS5 has:
7 Support Slots
1 BO Slot
1 Torpedo Slot
1 Gunner Slot
The Kai-Kou is difficult to speed cap. What makes it special is that it has the ability to launch TB's. (3 at a time; maximum of 8) The TB's have come in handy in HA's. Giving you the first strike option, you can damage/destroy strategic ships. Kitas, Subs, AA ships, even damaged BB's have all fallen by my Kai-Kou TB's. The negative to this is that the sonarman and planesman negative plane ability will make your tb's vulnerable to AAW.
The setup I use is: 1BO, 1Torper, 1Sonar, 1Planesman, 2TB pilots, 2 Engies, and 2 Reps (one on the gunner position) or 3 engies and 1 Rep (on the gunner position). Another setup is to not use the TB's at all. My setup for that is: 1BO, 1Torper, 1Sonar, 1Planesman, 4Engies, and 2Reps (one or Gunner position) or 5 engies and 1 rep (on the gunner position).
I would not advise using the 2nd torper on the SS5. Both the SS5 and the SS5.5 only has one torper position. However, SDE plans to come out with Premium Submarines and SS6's eventually. We don't know if they those submarine will 1 or 2 torpedo positons. Don't let the other torper fall too far behind.
One more thing; like all other ships, submarines benefit from having 0.2 belt. Good luck!