We'll about point 2, first time importing files. I'll create on our tracking system a new enhancement to get on importing the real date of document creation. I'm not sure if on next release it'll be implemented, because major issues of next release has been defined. We'll try.
About point 3 permissions. It could be some obfuscated. First must enable recursive change, and after it all operations are propagated to sub folders and document into.
About point 4. The answers is yes

it's some tedious to add a new mime-type, but must be done at this way because it's not only to set on mime configuration file it must be uploaded some icon. If you tell us about some new mime type, like other users suggested on this forum. On next release will put by default.