Hey, really great work on this!
I used to run low voltage wiring professionally, and that looks pretty great. One tip for next time: You can use clues such as that nail to help connect what you see “up top” with where you’re looking down below. The wall itself will have a “bottom plate”, a 2x4 laid flat horizontally across the floor, and it’s nailed through the floor and you’ll often see nails such as that one exactly where the wall is.
There’s no 100% hard and fast rules, but you can also look for the presence of other holes for things like electrical wire, or HVAC vents as clues too. One really important thing to remember is that 95% of the time, electrical outlets will be mounted directly to a stud. You can knock on the wall or remove the cover plate and use a small flat screwdriver to probe around and determine which side of the outlet is against the stud, and which is in an open wall space. That helps you plan where to drill down below to give you the best shot at hitting your intended location. If you remember that studs are generally 16” apart, it can help you visualize that section of the wall.
Avoid running wires close to windows, doors, or corners. Studs can do some really funky things in those spaces, and you’ll have a much harder time.
Totally accurate advice, but I haven’t usually seen it be terribly important in a residential setting because
They’re important considerations for sure, but I haven’t generally bumped up against them in the real world in typical houses.