1) I wasn't able to reproduce that error, but I am using the beta version. Would you mind installing it and seeing if this is still a problem?
2) Update should work. If you could give me FTP access and a url to reproduce the problem I could take a look and let you know what needs to be adjusted.
3) You can change the page layout type to "Standard" and it will allow you to add more columns.
The 406 error I haven't seen. I think it is because of mod_security that is installed on your server preventing database information from being shared with Dreamweaver. If I could get FTP access and your website url I would be able to try to reproduce the issue and see if there is something I can do to get it fixed.