With a multiplayer game you want to keep things moving so playing around with activation (clockwise activation, etc.) is always good especially if the players are not familiar with the rules.
Keep the special abilities fairly generic. You don't want to use some of the more exotic abilities as they take longer to get use out of and some players may feel cheated if they don't get a chance to use them. Your game seems mostly combat oriented so stick to the combat abilities.
Each player should have only a Grade 3 or Grade 2 and the rest should be Grade 1s. You could probably go with 3-4 Grade 1s per player.
Do not allow Grade 1s to Wait.
For your armored car, Have a Grade 1 Driver, Grade 1 gunner, and Grade 3 (or 2) officer in it.
Those are some of the ideas off the top of my head.