OK, I'll dance with you on this one, LOL!
#2 - You are right. A G5 will run Classic under Tiger or earlier. That's why I was specific when I said OS9 originally, and not Classic. Because, as you also mentioned, a G5 cannot boot OS9.
#3 - I was unaware of that, in the sense that it was modified. I got one job in July 2003 where the owner bought one of the first G5s, the 1.6Ghz model. It came with the OS you describe, Jaguar. But by 2004 most of the G5s for sale were running Panther. Which is why I used the word most. I would be piled on by all the denizens here for saying "all".
Personally, the best load out here if you are going to stay circa 2003-2004 would be Panther and QuarkXPress 6 with Photoshop 7, Acrobat Pro 6 and Illustrator 10. That's what I was running in 2003-2008 and it worked very well.