I have had good success keeping bichirs with large cichlids in the past. I would say that as long as the bichir is large enough to avoid being a meal, and vice versa, it will probably be fine.
Depends on the midas. As an example, my male midas would kill it, just for sport. Meal size had nothing to do with his killing sprees. He has always been a highly territorial fish, even as a juvenile. Hope for the best, but plan for the worst. A common theme when dealing with large aggro cichlids.
Jjaws7777 had a Pearsei that liked chewing on his bichirs until he separated them. A Midas is a good few levels nastier than a Pearsei. I am not saying it is impossible, I am just saying that someone on here tried it and chose to end the setup, not that it was a failure. I don't think any of the fish suffered lasting harm, just thought I should mention that someone tried something similar and decided it wasn't a good idea.
I have a single Barred Midas because of killings that lead to him being single. He also killed my WC red terrors. Very vicious he will spend his life alone