I dont know who vote for the 8 inf buy, but I think it is not good at all to only buy that. You get no conter-offensive power with those infantry.
I prefer buying one figher in the first round, and 2 inf and 2 art.
I usually send one of my fighter to the East, to help defend india in the first round(s) and to give an offensive power to the grunts i’ve moved to the japanese front. Sooner of later, after the us and Uk are strong enough against Japan, my fighter come back against germany. Having 3 figthers give you the opportunity to trade country with germany without letting him the chance of destroying to much troops.
You can stack a better army behing your line.