The push-ups are great for stability across the pectorals. I like forearm curls/reverse curls for lower arm strength and mass, and to stiffen the wrists when locked. Mixed with some bicep/tricep work for arm strength and stability. I also like spring-loaded grip strengtheners, you simply squeeze with your hand.
You can overdo this stuff. Just stay focused on the objective of building strength & stamina into muscle groups that support the pistol.