All these issues, especially #7, seem like an IIS config issue.
7) with directory browsing enabled, a request for http://mydomain.com/folder still shows a 404, does not show a directory listing
I would focus on this particular issue. If you can eventually get the directory to display the files underneath it then I think you will solve the problem.
Can you please show us what's inside your entire web.config file? Also, under IIS "Edit Error Page Settings" please set to "Detailed errors" if not already. We need more data here (logs, configs, screen shots, etc.)