Okay, this is the last one I’m taking because we’ve got to get on the road. I wouldn’t worry about the strike so much, while the proper strike can cause lots of internal injuries, the point where you learn how to do energy projection is in the theories behind board and brick breaking.
Martial arts students don’t just break boards because it looks cool and because it’s impressive, they’re actually learning how to project their force through an object so that the object breaks. You can do this with anything really, I once saw my master bend a re-barb pole with the soft tissue under his throat and there was that time he broke a baseball bat with his shin.
But that’s really where you start learning about energy projection through something or someone. “Easy” internal injury spots are under the chest where you could collapse the cartilage holding up someone’s lungs during a strike to the solar plexus (the xiphoid process, I think) . The back: striking the kidneys. The side: cracking the ribs hard enough to send them inwards into the lungs, the stomach, and the intestines. It’s hard to do that one with your hand though, Sambo has a strike where they do the sidekick while grasping the other person’s hand to hold them in place and just plow into the person’s side.
But I’ll be honest, deep tissue strikes are hard to pull off without years and years of specialized training.
The fact that you’re worrying about it is a good sign. As long as you respect your style, respect it’s capacity for violence, what you can do to yourself and others, you should be okay.