Personally I would avoid the red devil, I think the texas and the devil would likely clash, similar body shapes, both would want to be dominant. Salvini and firemouth should be decent choices, though FM might be a bit outmatched aggression wise
I would let the texas be the largest cichlid, and replace the red devil with two or three other 6-7" max cichlids. The texas will be dominant, and there will be enough of the smaller fish to spread the aggression around. Some species to look into:
Cutteri
panamensis
Honduran red point
centrarchus
I'd also do large tetras like Buenos aires instead of the silver dollars, the SD"s get real big and will add a lot of bioload for dithers.