I usually add all the files to the import array, only change it to one import per line to make it easier to read.
Have not used autoloading in sage but I don’t believe the files will be automatically loaded, they will be loaded when used/needed. You have to use the class somewhere for it to load. Something like
Post_Types::register()
or
new Post_Types()
in setup.php maybe?
The app folder is pretty full of files in many of my projects so I would probably change it to
"psr-4": {
"App\\": "app/classes/"
}