but if you had to choose between the two then artillery. they should really never have any territories left that are more than two spaces away from india anyways. Artillery allow you the ability to attack, while mech inf give you the ability to move lots. Although India should do little of each, it’s conceivable to be doing an attack or two before you die. But not a huge movement.
You seem to have it all correct. Your planes can not hit the subs because you do not have a destroyer in the battle. Japan may not remove them as a casualty, if you hit with your planes.
The Japanese subs also don’t get to shoot, if all you have fighting in the naval portion of this attack are planes.
I amphibiosly attack Philipines. There is a transport in the sea zone. My BBs can ignore the transport and do shore bombardment, while I hit the transport with planes and/or other ships?
No. If you attack the transport, everything attacks it. You can either kill it or bombard, not both.
on a related note, I certanly hope the UK is one territory in Europe 1940. So they can scramble to protect it just as japan does
That would mean that Britain could only touch one sea zone (unless they want to make an exception rule) and would almost completely rule out any possibility of a German naval attack or Sea Lion attack.
It would probably make it too easy to build up and invasion force to clobber Germany since the US can just stack up planes in England and they can defend the entire Brit fleet as well.