You could do it that way; I think the only drawback would be that everyone would have access to everyone else’s media uploads, but there may be a way to adjust permissions so that someone in an author role would only have access to media they’ve uploaded. I haven’t looked at that in a long time but that sort of seems like that was an option, or certainly could be a plugin.

I’m not sure if there’s a default way to let people sign up as authors, but from a spam-prevention perspective it might be better to let people sign up as commenters and then request their accounts be promoted to authors; I wouldn’t imagine an automated WordPress spam bot would ever understand that it could request promotion to author, so anyone who asks is probably human.

Overall that’s probably going to be a simpler method, just needing some relatively minor tweaks from a typical Wordpress installation.