Did you try right-clicking on the Hall of Champions logo and using "Save image as . . . " (or your browser's equivalent) from the https://www.drivethrurpg.com/cc/28/hall-of-champions link? It saves as 96 dpi for me.
As to your second question--the guidelines and types of content information seem to indicate that you can publish characters that you created for other systems--as long as you retained the rights to them. If I'm wrong, I'm sure someone here will correct me. I base this opinion on these lines:
From the "What Types of Content Can I Create?" section: "Characters: Now you can sell the villains, monsters, gods, animals, and heroes you’ve cleverly created!"
From the "What Types of Content Are Forbidden?" section: "Other People’s IP: You do not have permission (or we the right) to release work based on the intellectual property of other people or companies as part of Hall of Champions. If you wish to for example show other fans your Champions 6th Edition write up of DC Comic’s character Green Lantern, please do so FOR FREE on the Hero Games website forums (https://www.herogames.com/forums/) or in some other location. But not here!