There’s been a lot of discussion on CAs. Two of the more popular opinions seem to be letting them transport 1 Marine/Elite type unit for amphibious attack. The other is giving it some sort of AA capability.
As far as Mech, their mobility is their worth imo. Combine them with Bombers for striking power and they can be quite effective. Some countries will use them more than others. Germany and JPN and UK coming up out of Africa probably the most. I tend to not as much with USA as I like Inf/Arty to establish a beachhead in Western Europe. Then some speed units out of the factories, especially if I’m in Norway. I don’t usually go into Africa with them, but you’d want speed there too imo.
It’s nice to have a small mechanized force with Russia if you can afford it. Just having the threat of a Quick Reaction Force can limit some moves by the enemy. Or at least make them think about it.
Usually like a 2:1 ratio with Armor. Especially Germany. Not sure how others do it. I should probably study some more games others have played. It seems I always get sidetracked doing other stuff though 🙂