Great course so far, I am really enjoying it!
I have to say though, that I’m not a big fan of a physics-based combat system in an RTS (using actual projectile collisions to do damage). The main reason is that there is no way for the player to affect the aim of his units. A very fast unit microed by a skilled player could be very difficult to kill in this system.
I think the projectile-based system might be used for e.g. siege units meant for destroying buildings, but in unit on unit combat, a hit should be in my opinion, by deafult, guaranteed.