Hi Anders, Federico,
F: Not Notes. No such thing I have seen. You probably mean TextEdit, the basic standard supplied text editor. It's been a while since I used my Mac for lilypond, so I can't remember, but I think any text editor could be made to work. Since it now cannot due to Apple's decision (why do they keep reducing functionality?) it is no longer relevant.
A: You can get tab completion plugins for PowerShell if you hunt around.
Also, as mentioned, Skim works for this purpose last time I used it.
Andrew