Re 2) I'm running a multi user homebrew setup for years. I have my users (personal and various work accounts) live under the "Local" Group and do

``` sudo chmod -R 770 /usr/local/ sudo chmod -R +a "group:Local allow delete,readattr,writeattr,readextattr,writeextattr,list,search,add_file,add_subdirectory,delete_child,file_inherit,directory_inherit" /usr/local/ ```

I remember sometimes running into permissions issues but nothing re-running that command didn't fix.