165g tank with 55g sump - Breeding suggestions?

[Abemas]

I have a 165g tank with a 55g sump that currently holds 5 large fancy goldfish and its main purpose is to "fuel" an aquaponics grow bed in my front yard (water is pumped outdoors and then gravity drains back to the tank.) This is my second year with the tank and I moved it inside so I don't have to deal with needing to relocate the fish every winter. Now that it is in our home I'd like to do something more exciting with the tank and perhaps do some breeding (thought the kids might enjoy that.) The tank is unheated but I'm guessing it will stay between 65 and 75 depending on how much the growbed warms the water when it is in that part of the loop. Water is on the hard side but the goldfish seem to do very well. Tank is only viewable from the top and the goldfish don't have to stay. Any suggestions on what do in here?