Your catfish will both need to be in a 10'x5' tank minimum.
Arowana need a 8' tank when it is fully grown.
Reticulated stingrays need a 180 gallon tank,and are not advised for beginers.If yours are not retics,they need a 8' tank as well.
These fish,if adequately feed,will outgrow that tank in a few months.
What are you planning on doing with them when that happens?
75 gallons is big enough for your JD,and maybe one more larger SA/CA cichlid.It depends on the fish's temperment if it will tollerate a tank mate though.