My view:
It would depend on the background knowledge.
If you don't have anyknowledge/experience with flight in general, learn the principles of flight first, experience them.
Get systems knowledge (both general and specific).
THEN jump into combat.
But my tip first and foremost.. learn to fly WITHOUT the TGP!
If at a later point you need to spot something QUICKLY, you will be able to, where as if you learned combat just on the TGP you won't. IIRC, real A-10 student pilots only get to fly with the TGP at a later stage in their training.