Short: yes you can do that.
to be able to see all blog posts
the default editor role can manage to see all posts
be able to post in the blog
again the default editor role can manage to see all posts
be able to add new “portfolio galleries” and “portfolio pages” and have them automatically tagged with > the “artist” taxonomy with the same value as their name (i.e. John Smith).
For that you can use the save_post hook and automatically add there username as taxonomy.
be able to only view portfolio pages and galleries that belong to them
(i.e. John Smith will only see > portfolio pages and galleries that are
marked with Artist = “John Smith”)
when registering post types you can define capabilities for that post type and you need to define edit_others_posts as false, also make sure that your post type supports author.
Finally we would also like to have a
couple of “super admins” that will
have access to every post on the site.
the default admin role is your friend in this case.
basically most of your issues are with Roles and Capabilities
hope this helps