Ideas:
You can only hold like 5 Cards, and that number can go up if you have more Technology… The cards are either 1 time use (no cost) or multiple use (cost per use)… Like your suggestions… I would imagine we have “abstract” (“skill”) abilities and “concrete” (unit)… In fact instead of having National Advantages you could have cards play those… Maybe draw 1 card a turn can be increased by tech? some ideas for Cards:
Russia:
Katyusha
Fanaticism
Siberian Forces
Urban Defense
Germany:
Rail Guns
Heavy Tanks
Storm Troopers
AA Artillery
Britain:
SAS
Commandos
Home Guard
Japan:
Kamikazi (so it won’t cost so much)
I have run out of ideas so someone else please pick up the ball! :-D
GG