Management of mail folders

When you move a folder or a set of folder up in hierarchy, you can’t just drop it on the folder. You need to point between the folders to insert it. It took a while before I did find out how to manage the folders. I would prefer if you’re able to drop the folder in to another. (As in the outlook client)Is it only possible to create folders in the “folders” container, and not the inbox or other folders?

I miss the ability to see the size of a folder(s) like the Outlook client.