I've toyed around with stealth before. I generally laid out how each of the senses, including smell, can be used to detect and how you could avoid being seen. I also added in that failing a stealth check against passive perception only put the target on edge, and then a contest had to begin for perceiver and Stealth character.

Theres a lot of ways you can do this and i think you're solutions are fine, but I'd ask how, if at all, you'd plan to handle stealth assassinations. Realistically if i attack from stealth i can kill almost anyone in Real Life. In 5e, you could essentially stub their toe as the first attack of a 20 minute battle. This wasn't anything I could find a solution to in 5e or most HP based RPGs without heavily modifying or making my own RPG altogether.


Something to think about, and get back to me if you find a solution.