And between functions? 

 I wouldn't. I'm old school I guess, I prefer everything up front.  

 Structs all to front gives you an idea of what you're working with.

What about pub vs private structs /functions? 

 when having several structs I'd say it's mostly prettier moving them to their own files, because then you can use the filename to re-find your structs. 

 I do this. Structs above impls and functions. 

New structs that come unto scope below existing functions but above functions that use them.

There's while folder and module structure you can consider too for organization.