My usual setup for single player is 7 INF + 2 ART (+ENG, ART, LOG, REC), and past 1940 I slowly start to replace 1 INF in that template with 1 TD. In 1941 I add support R-ART into the last slot.
In terms of pure defensive power, I'd recommend to go with Grand Battle Plan - it scales really well with ENG and the defensive leader traits and allows you to create powerful defensive lines while stationary.
In terms of pure defensive power, I'd recommend to go with Grand Battle Plan - it scales really well with ENG and the defensive leader traits and allows you to create powerful defensive lines while stationary.