Theoretical Early Game Stack

Well, for one thing: you might be better off only combining the AT & Infantry , because those troops are going to seriously slow down your faster AC units.

You would also need AA to not get killed from the air. Most people use too few AA in stacks like this; one or two just isn't enough against a serious human opponent.

Since you're referring to "early game", prior to Med.Tanks (MTs), I'm not sure if one would have the Manpower to produce much of an attacking force that's capable of fighting with the speed one might need to make up for the lack of numbers. Both INF and ATs are Manpower heavy compared to LTs.

However, as a defensive force, your INF, AT, AC makeup would be good; especially if the ratios were adjusted for terrain type.

I'd still use the ACs to scout, take unguarded territory, and then rejoin the stack for fighting. Perhaps the ACs could temporarily form a stack, to take lightly guarded territory, and then disperse to continue scouting.

if you don't have any antiair the first Tactical Bomber you meet will make short work of that combination

Antitank research takes 30 minutes, and you don't need infrastructure to build antitank, so they are a good candidate for first day production while your infrastructure is being built.

Artillery are good to have in stacks early most of the time, depending on your enemy.

Antiair are a necessary part of any stack that leaves my core. Don't leave home without it.

The manpower constraints mentioned are valid, and require quickly building a L2 barracks in your top manpower city. I typically find when trying to build the cheap high manpower units that I have surplus resources to spend on economic development.