So, this would be my suggestion, please note it's a rough draft and looks ugly, I've made this in like 15 minutes
1. The Icon Color is the player color (might get lost the less HP the ship has though)
2. Shape of the unit is represented
3. I ignored that requirement, there's still room for icons on the bottom left for example
4. Mark level is prominently displayed
5. Health is displayed with the fill of the icon itself
6. Selected squads are icon 1 and 2 (yellow border)
7. Shielded squads have a shield icon on the top right
8. Cloaked squads have an eye icon on the top left
9. I tried scaling it down to 10% and it's still sort of visible
10. If you use vectors instead of bitmaps you could scale this up easily and with that increase information available e.g. implement 11 at a higher zoom level.
An alternative would be the healthbars in a vertical position next to the ship graphic and have it filled at all times.
I feel like the *most* important information that you *need* to see at a glance is:
1) what is that ship
2) what mark level does it have
Everything else is just fluff that helps micromanaging mostly and is just *not* that important for the typical player. You still have dozens and hundreds of squads.
-Is the health of a single squad so important to display it permanently?
-Is it so important to know at all times that the unit is under a shield? (You can see it visually)
Just a few thoughts.