Depends on play style. I usually have something like 2 recon, 4 infantry, 4 artillery, 4 tank, 2 anti-tank self-propelled battalions, 4 fighter planes. This is what I try to start with and have them from the first scenarios with fighter planes being purchased last if I have the prestige. Then I increase accordingly except recon and fighter planes. I always update core to latest available and over-strength.  Depending on scenarios I usually choose a side of the map where I deploy most of my core. I stall the enemy with auxiliary units and push with core in one region. If the scenario duration is short or there is no space for maneuvers I will need to deploy core in multiple places. Then I push to objectives but I don't chase/get stuck fighting enemy units after I break through a line, that's something for auxiliaries or I buy a cheap unit/infantry to defend an objective. I always try to have a small combined arms group moving (ie 1 infantry 1 arty maybe 1 tank). 

As for ships/naval transport this has always been bad, even in original game.  The naval part is really overpowered on attack, I try to deploy a minimal group and move it fast to land, then another (in waves). I use my naval attack ships to stall and keep enemy battleships/cruisers/destroyers away from my transports.