Please verify that the fileserver (Management -> Services and Updates -> Service) is running and that your have specified also the correct domain name as defined under (Services -> File Server -> Configuration).
Please make sure that you also have at least changed the default password of the user root. This is a required step before one can join PC's into the domain. Use this changed password when joining the domain with the root user.
Also check if your WINS is setup correctly, and that you can ping the server by name from the client you try to join (ping <servername>).

The netlogon share is non-browsable. This means that it cannot be viewed by scrolling from the \\<servername>. However it can be accessed via \\<servername>\netlogon. You need to be administrator to have write access this netlogon share. All other users have read access on this netlogon share.

Yes, that is possible as long as you store the script file (containing the script code allowing for personalized logon settings) in the netlogon share. This script will be executed when logging into the domain. Logon scripts are typical bat files (logon.bat).

It is possible the client still remembers the previous file server connection. Therefore go to Start -> Run. Type cmd in order to launch the MD-DOS console. Type in the following command line "net use * /d" in order to release all the file server connections. Try to connect again to the concerned file share).