From: Ashington, England.
As a very experienced IJN player, I thought I would pass on my tips on getting the best out of the Jap navy.
1) Aircraft carriers
By far your most valuable assets, get as much use out of them as you can in 42 because by the middle of 43 they probably will be easy VPs for an experienced Allied player.
I tend to group them in groups of 2 CV plus a CVL per TF, usually matching pairs, Shokaku/Zuikaku/Shoho, Akagi/Kaga/Ryujo, Soryu/Hiryu/Zuiho, Junyo/Hiyo/Ryuho. I also throw in a Kongo class BB to divert a few of the attacking a/c, a CS within the slower speed CV TFs and then add DDs. I find about 10-12 ships per TF is adequate. Set the slowest speed TF with its destination and have the others follow. Thus you get maximum CAP protection for all your fleets whilst avoiding the airstrike co-ordination penalty. When the smaller CVEs arrive in late 42 I usually put a Zero sqd aboard to boost CAP.
Do not bother putting any CA or CL in a CV TF as they offer little in AA value compared to US cruisers. They are much more useful in surface combat fleets. The exception is the CL Oyodo which arrives in early 43, it has good AA and no torpedoes so is not much use in a surface fight.
When it comes to the actual CV battle itself, a lot is down to chance, but you can increase the odds in your favour:
Firstly you must spot the enemy carriers. Asign all your CS based floatplanes to naval search (Chitose and Chiyoda's complement should be more than enough). NEVER put any Kates on naval search, these are your main ship killers and you want every single one sent out to attack. Only use Vals on search if you are low on floatplanes.
Try to run a low % CAP until the day you expect action. A badly fatigued CAP performs much worse than a fresh one. As to overall CAP level for the day of action, it depends on how many fighters you have and what you expect the enemy to put up against you. Bare in mind though that you want as many of your precious high exp strike pilots to get through the CAP to attack, as many will not get a second chance, so they get a strong escort from me. Personally I usually run about 30% CAP....in the end no matter how many fighters you have over your carriers, some SBDs and TBFs are going to get through......
Early in the game you get 2 Rufe FF sqds. Put these aboard the CS Nisshin. It gives an extra 18 a/c on CAP, they are not as good as Zeros but every little helps!
Try and fight within range of a friendly airfield. Your airgroups are just as precious as their carrier..... if one is sunk the survivors of its air group can be disbanded into other groups to make up for losses elsewhere, keeping the overall exp of the group high.