A few questions.

How do you make anything for the hud, such as Shield Meter, Gun/Ammo portrait?

Is it possible to have a syncing door?

Is it possible to have a detach turret script?

http://ghost.halomaps.org/

yes and yes

I see Ammo Meter, Pickup Icon, no shield meter, radar or anything else.

the rest are made the same way, you just have to open the Hud_globals or weapon HUD and re-link to your new bitmap.

So I just make like it's an Ammo Meter and just use it for the shield bar?

I'm sure looking through the tags would answer your question.