Good question. He will be more than comfortable in that tank for life. Personally I wouldn't put more fish in...only because I wouldn't want to take a chance on him getting damaged. I keep this fish for shows.
Can they live with other fish? A female divided...sure. Difficult to say if you could enter another fish without a turf war. Either way you wouldn't want..or should...add more fish of any kind this size in a 75 gallon tank. Cramped environment and stress would take its toll.