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.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence