1. I'm in the process of reading the manual but haven't installed GPO4 yet.
It says in the manual to go to the Garritan site for tutorials. As far as I've noticed there are no GPO4 tutorials yet but tens of tutorials for the Kontakt player.
My suggestion is to split between the tutorials for the Kontakt and ARIA versions. Put them on different addresses so that they won't clutter one another.
2. When are there expected to be ARIA tutorials?
3. Will those be videos as well as written?
4. The manual looks very well written. Good job on that. I like the fact that there are pictures in many sections of the maual showing what they are talking about. This way there is no need to be in front of the computer in order to understand what's being said.