6* Archangel, Cosmic Ghost Rider, Human Torch and Warlock are all great for story content so I’d start with them. Don’t upgrade a 5* where you’ve got the 6* version. You could probably add bastion and longshot to that list. You’ve got others like Shuri, Silk, Red Skull and Spider Ham that will be great if you start doing battlegrounds and for other stuff. It looks a great starting point and you’ve got enough variety there to get you through chapter 6. From your 5* Medusa is invaluable for all kinds of content if you can awaken her although I’d try as much as you can to focus on your 6* champs as they’ll work for a long time to come.