that is a pretty bad plan
On R1, I usually buy 3 inf 3 tanks
on R2 I usually 4 inf + art + ftr
if he buys 16 tanks on G2, the game should be over, as long as you create stacks, and dont lose battles (you should never lose battles, if you do, then you placed your units wrong, or are in a no retreat scenario)
just buy like 8 inf + 1 tank or so, you should be fine on R3