To sign in, use your existing MySonicWall account. To create a free MySonicWall account click "Register".
It is to notify of policy changes, maintenance etc.
If it's a domain computer, and you have a login script currently capable of doing that already, you should be able to have NetExtender run the script on login using the Connection Scripts dialog in Properties in NetExtender.
I always assumed this would be possible using JUST a SSLVPN client, but never found a way to do it... Hopefully we can get a direct answer.
One can do this with Cisco's AnyConnect client...