I ended up getting a 150 long. Would it be possible to keep a Barred Midas and Green Terror. If not a Beani instead of the Green Terror?

I think your best bet of keeping fish with the midas in the 150 is convicts. They are small enough that he won't see them as too much of a threat, and they are tough and pretty smart. They should be able to survive in there with him. I would get 5 or so and let them do their thing, they might breed as well so be prepared to do something with the fry if they aren't eaten.
This is a good point. You could just go all-male convicts, they are easy to sex and males would make better tankmates anyway, females stay a little bit small to live with a full grown midas.Or the midas might breed with one of the convicts and kill everyone else in the tank when the two spawn to make hybrid fry.
Midas are one of those fish (like parachromis species), that have a high chance of claiming 6 feet of territory all to themselves.
What other fish could hold its own with the Midas that I could get