4 production line challenge

im planning on playing Germany or US I havnt decided that yet but the main challenge is going to be only 4 production lines allowed and if I somehow reach factory limit for those 4 lines then it'll just turn into only 4 things being produced at once. To make things a tad bit easier I can swap whats being produced so im feeling early game needs to be focused on trains and get a good stockpile then switch it to something like trucks. I am allowed to use stolen equipment and vehicles as well.

1. infantry weapons (duh this is needed)

2. mabye support equipment

3. ?

4. ?

Im sure I probably need something to win the Air war so I need to either make AA or airplanes but im stuck on which to choose. AA would help make my troops stronger and deal damage to enemy planes and stop enemy cas but if I focus on fighters then I can win the air battle and get green air then use captured cas planes to bombarded the enemy.

I feel like trucks are more important then Tanks because with trucks I can do motorized supply lines and make motorized divisions while Tanks are really good to but then id rely on normal supply lines.