You should create a Page not a group. There's no way to promote groups because they are hidden on profiles and they are private activity. People can't Like a group, they have to click to join and you have to approve them. Plus, people have to click through folders and it's not as visually interesting as a Page.
I create pre-made covers and would be interested in participating on a page. I wouldn't guess that there'd be too many designers. You could make them administrators of the page. I share several joint pages. It's not that big of a deal. It would be a showcase for covers with links to sites, not a place where people buy them, so I don't share the same concern as Humblenations. I wouldn't put up every cover on there. Just a a few a week to show my range.
I create pre-made covers and would be interested in participating on a page. I wouldn't guess that there'd be too many designers. You could make them administrators of the page. I share several joint pages. It's not that big of a deal. It would be a showcase for covers with links to sites, not a place where people buy them, so I don't share the same concern as Humblenations. I wouldn't put up every cover on there. Just a a few a week to show my range.