Lots of food for thought here. I've never tried modifying units or the rules but this has inspired me to try. Where would I find this ww2 mod?
I play on a 27" iMac with 24Gb RAM so use a game size of 125 by 125 and have 3 opponents each enhanced standard AI, everybody starts with one city. My initial priority is expansion capacity so I build armour which explore trying to find a city to conquer and build transports. I produce a single bomber to explore while I am building up invasion capacity. On this size of board finding the enemy quickly is vital so I try to build surveillance satellites as soon as I can and meanwhile build bombers which I throw away on 24 move reconnaissance missions. Similarly I build destroyers as soon as I can so they can perform high speed exploration.
I find cruisers and battleships useful for defending the first couple of cities taken on an enemy island. I also use sea bees or engineers to construct oilfields, ports and roads to speed up transit across poor terrain. Due to their anaemic range I have no use for missiles or nukes. I find air transports too slow to be useful and I have never built an aircraft carrier. In old empire I used carrier loaded with patrolling fighters for rapid exploration, now there are satellites.
I quite like the capital kill variant as this means you have to carry out missions inside enemy territory in order to take out one city.