The second attachment is a library I am currently working on that 
implement a functional dired side window and its windmove bindings 
in 200 loc, so you can eventually try it and feel what I am 
requesting.
I wrote it for testing purposes for bug#48493 so some of its 
functionalities relies on fixes that are not yet available, and it 
is less about dired in a side window than implementing local 
bindings on couples of buffer/windows.