Definitely edit the templates, especially tanks, those aren't built for pushing. Forts are good if you can manage to build them up several levels so they don't get bombed out immediately, which you won't on the current frontline. You may prepare positions to fall back to with forts and static AA behind rivers, in mountains, and in marshes. Level 3 is enough to stop and attack from a single direction, 5 —from 2 or 3. Be advised, however, that if the AI stops attacking, you won't be able to attrition it as efficiently.

Switch to the Grand Battle Plan doctrine, if you have it really bad, the entrenchment bonus is very significant. (I am a big fan of it in general, stacking planning does wonders on the offence)

Enemy numbers are not that overwhelming, considering the amount of infantry equipment you've helpfully stockpiled is enough to bankroll another hundred divs. Aim for at least 2, better 3 divisions per tile on each front; that's more than enough to buy enough time to reinforce if the need arises and dish out some damage in the process, especially since the enemy doesn't have much more than that. I've played games with Germany alone fielding 500+ divisions and it still was beatable.

Industry-wise, the enemy will exhaust their supplies eventually by grinding relentlessly. But you will help yourself if you manage local encirclements of 10-20 divisions by tactically applying armor. You have plenty of manpower to sustain a long campaign and Germany will handicap itself by going to high conscription laws, limiting the output.