IMO a 100 gallon is too small for a large Oscar and Midas. A Tex will grow smaller but it will still make the tank even more cramped.The other thing to consider is the aggression level in this tank. Both Midas and Texas Cichlids can be aggressive. Oscars are usually more docile but they too can be aggressive at times. If one of these fish becomes aggressive it could cause the set up to fail. Due to the potential adult sizes of the fish in question, the amount of swimming space they require, and their temperament, I think you should pass on this idea and try some other cichlids in the 100.