I don't know how much detailed information I can give you, but I'll try to help at least.
Operationally, and to a degree strategically, in planning and executing your invasions early on, don't worry too much about allied airpower. I'm sure you noticed playing allied vs AI that pretty much all the bomber groups in the DEI-Malaya-PI area are very low experience and basically suck. So, while you shouldn't risk anything unnecessarily, keep in mind their hit rate will be terrible, and only the few torp bombers in the area pose a real threat to your warships. Also remeber that Japan has a lot of transports to work with (but fewer tankers) so losing some will not hurt your war effort much.
That being said, in my experience with PBEM, the biggest unexpected threat to invasion forces in that area was allied surface combat groups, which often include force Z. Against a human player expect full speed hit and run tactics and creative positioning of where they will attack. So for this reason, don't let your invasion forces get too exposed and go without escort. This is the real purpose of the mini KB.
One big advantage that Japan has is a lot of recon planes available, so use them to see what bases have been reinforced and what bases have been abandoned.
Of course as is really the same with the allies, be sure to bring enough forces that you know you will overcome the enemy.
Oh, and in regard to your actual questions:
1. The 2nd Day strike may finish off some ships, but remember that the ships in PH aren't really the ones you should worry about. Those old BB's are terribly slow and are nearly useless without air cover, so sinking them is actually not a top priority for your CV's. Moreover, any losses to your high exp, nearly irreplaceable IJN pilot corps is unacceptable. You get so few of these guys each month, and those are actually desperately needed for land based squadrons as well. Save your pilots for when you really need them: against Allied CV's!
2. Take out any tank units, in large groups they are fast and deadly. Other than that, there are really just normal army strength units.
3. One Division will eventually take out Hong Kong, and arty will help somewhat, but Jap arty is pretty bad. However, I would recommend sending both Div's that are at Canton, because that should take out Hong Kong quite quickly. Don't worry about a counterattack too much, Canton is an urban hex and you would be defending against very poor chinese units.
< Message edited by Xxzard -- 7/16/2009 4:21:10 AM >