To question 1, yes, sudo su is global, you only need to run it once, then just do all your commands, in that terminal session. Now if you exit that terminal or switch to another, you will have to run it again. The password it asks for is the one for the user issuing the command, for instance your password.
To question 2, I currently do not have anything that uses HDMI. But from reading some of nite_man's posts, using the latest ATI Catalyst driver, this looks very likely. I intend on using a DVI to Component video cable or an adapter with the ATI HD3200 video chipset, I currently am using an Nvidia 7200 GS on this MD, but I have need for that elsewhere, so I will get started on getting the ATI bits working this week yet.
I will post my findings, and howto after I get it done. And will post the completion here in the forums. So hang in there, I might be able to acquire a device (HDTV) to test the HDMI, but I don't want to say for sure yet. Look for the posts from nite_man, I think he has it sorted.