That email feature is somethin Itch should scratch or overhaul.
Also, using it to notify followers is moot. They get your stuff in their feed already. There are some complain threads about people getting lots of emails after buying those huge bundles.
As for portfolio, a profile page is mostly just a website. You can include a link and picture and text.
I agree that adding contributors only as full admins is not what many people want. But it might be required legally. There is a thing like joined copyright. But if some people do engage in this, they really do have all the rights and are both responsible, as far as I know.
So maybe a better feature would be to simply add a contributor line, instead of allowing multiple authors. But as I said, maybe, if they are added as authors, they must have same rights.