it is entiely possible that a midas pair would take over an entire 150, would be the same with flowerhorns, festae or any of the large cichlids. I really wouldnt be surprised if it did happen, but there are many cichlids to look at when you have a tank that size, some other options to consider besides the midas are Nandopsis Haitiensis, any pike from the Lugubris group of pikes they tend to average between 12-18 inches long, parachromis friedrichsthalli, or even red tiger motas. just some other options to look into as well, as for locating the fish best place to go in the US is at this link Jeff Rapps is the best that there is. Jeff Rapps Stock Page.
I would say, Red Devil, Female Red Terror, Texas and a Jaguar, BUT! this fish must be brought as 3" and no larger so there for they can grow up with each other and there will be much less fighting going on. Just remember when these guys grow up your tank will look full.