How much programming is needed to connect the visual, audio
and overall functioning of an average yet high tier game?
It mainly depends on what you define by a “high tier game” and how good are your programming skills, so there is no general answer to your question.
Honestly you can go pretty far with just blueprints. I started with zero code and got movement, UI and basic audio hooked up in a few weeks. C++ only really matters once you need heavy performance or custom systems.