This is most likely done through the data editor, but will over-lap with the triggers as well.
I'd like to have a unit's command card have buttons that have a charge (counter) and I can replenish this via triggers.
This would be like how in the campaign Jimmy can pick up grenades.

I'd like to have the icons be non-interactive so they are used to give the player a quick read on their ammo pool for that unit.

Can anyone give me a link to a decent tutorial about this?
Thanks.

In theory, can't you just create a ability with charges and make it have a requirement so it is grayed out in the command card?
I may create a map to test this out when I have time later (tomorrow, or the day after).

Yea that should work.
I was thinking of doing the flat icon buttons, like how Colossi/Reapers have the cliff walk/jump icon but it's not a button nor is it disabled.

I don't think that will work, those are Passive buttons which can't be given commands to link them to an ability, the most you can do is put a requirement on them to grey them out.

Also you shouldn't necessarily have to disable the ability and thus grey out the button, just make sure the charges ability is of the Effect Instant type and that it doesn't do anything or consume any charges when used, then nothing happens when you click it and it's not greyed out either.