Upper lip only injections?

Thank you for sharing your questions and photographs.  Though you did not post any goal photographs I think you will likely need less than a half syringe to achieve a very nice result as your lips already have a nice shape and volume.  You can always add volume with touch-ups until satisfied with the results.  Hope this helps.

Yes, you could treat upper lip with 0.5 cc and if well done, will appear natural, not "ducky."  Photos don't show relationship between upper lip and teeth, an important determinant that, in addition to your present volume and desired result, should guide injection technique and distribution.