How much should I take for the adrenals and should I take it on an empty stomach?

A half to full teaspoon three times daily at least 20 minutes before meals.

Also, can I just stop taking the 4 grams synthetic Vitamin C I'm already taking straight away (2x 2 tablets a day) or do I need to wean myself off it slowly?

It would be best to reduce it since that is a very high amount you are taking and suddenly stopping could lead to dumping of vitamin C ("rebound scurvy").

Finally, what aspect of adrenal fatigue has made me lose fat on my face (I'm 27), mostly my forehead and under my eyes (look shallow and are also dark) and is it reversible as the adrenals heal? Is this connected to the liver possibly?

I would suspect two things going on.  The adrenal dysfunction would lead to hormone imbalances that would lead to the loss of facial fat and the adrenal dysfunction would also contribute to a loss of structural proteins.

Thanks.

PS: What about muscle pain due to AF, why is it really bad in cold weather but pretty much non-existant in warm weather? Is it due to poor circulation?

More likely from the increased inflammation adrenal dysfunction causes.