3 different kinds of tanks? 2 different kinds of fighters? 2 different kinds of bombers? You do know this is Axis and Allies the board game. Not Axis and Allies minis.
British heavy and French light tanks were completely different vehicles with different roles.
There was a constant arms race in the air, with supremacy changing several times as opposing sides introduced new and better aircraft designs.
How can you have no bombers in the game? This is the perfect definition of a tech - an effective new type of unit introduced about halfway through the conflict.
OK, I was going a little too far (I want loads of cool aircraft minis). To cut it down to 6 (why is 6 such a sacred number - is it the number of The Lord Larry?)
1. Gas shells
2. Tanks (in this case it would have to be the British and German heavies, ignoring the French FT17 light model that was produced in greater numbers than all the other types put together)
3. Anti-Aircraft guns
4. Bombers
5. At least one more type of aircraft. This depends on which is represented initially; but there should be a “reconnaissance” type (2 seater, long-range, poorly armed) and a fighter type (1 seater, short-range, armed with ffsmgs). The Rec planes should be the starting units, the first effective fighters introduced in 1915 (Fokker Scourge) being the tech.
6. Rail Guns
I don’t see that forts are techs - there were plenty around in 1914. I’m assuming that places like Galicia, Belgium and Eastern France would have them at setup.