75 gallon aquarium.......?

You have two choices with such an amount of water, lots and lots of small fish or larger cichlids such as the blood parrot. Sometimes if fish have been grown from small together they do not see other tank mates as food so you may have this situation with your parrot. Its all a little market garden your tank but I have seen more odd mixes work. You seem to already know your stuff so I will wish you luck. Personally I'd go for 25 cardinals rather than Neon's but check shops PH first and try and get ones that are used to hard water of you live in the south east UK