Thanks for your reply!
Yes for me thats totally fine, thank you!
You could just check both “edit_post” and ‘upload_files’, then you have what you want I think. Note that (in case you re interested in caps) there is a difference between ‘edit_post’ and ‘edit_posts’. I think its a little smarter to use edit_post and pass the attachment_id as an argument, but edit_posts also kinda does the job well. Only FYI, there is a great article from Justin Tadlock about caps which I personally found very helpful, as the documentation about caps in the wp codex is not too detailed.
https://justintadlock.com/archives/2010/07/10/meta-capabilities-for-custom-post-types
