For Japan:
SZ 6(obvious)
SZ 35(central location of Japanese Empire; can reach Queensland, Burma, Japan, and Carolines.
SZ 33(Easternmost base; threatens Hawaii and Sydney and protects japan
SZ 37( Can reach India and most of Australia from here)
Allies:
SZ 54(This is the NB where both ANZAC and the US threaten the DEI and the Phil from)
SZ 26(US, on the way to Z54, threatens SZ 6 and SZ 33)
SZ 63(Can still reach java, is further out of reach of Japan, and can be protected with scramble)