Did you have them outside last week when the high was 20 degrees? If so, that is one tough group of fish. A cheap sponge filter attached to your pump is one filtration option. Where's the current bacteria living? You probably know this but I'll say it in case other people reading decide to start a project similar, you do not want to remove your filter and clean it completely, that will wipe out your good bacteria and the water chemistry will get mucked up. Regarding the number of fish, there is not an exact number, but since you have aquarium experience I'm confident you will find the right number. But certainly less fish in the Summer than the other 3 seasons since it is outdoors.
Why do you have the Peacock in a 60gl and not the 110? Hope you can post a picture of the Peacock, they are beautiful fish. I'm going to try them once my stock gets lower or I set up another tank. I'd also like to see what kind of Sunfish? I have native aquariums and Sunfish make excellent options for hardy, colorful, entertaining fish to keep. A few well chosen Sunfish would compliment your Peacock tank nicely, not all Sunfish were created equal. Some just don't look good in an aquarium. Creek living Green Sunfish with their big mouthes and orange fins would look awesome and like a Peacocks cousin. Brightly colored Longear (Rainbow Sunfish) would be nice and are easy to find, and if you catch a Hybrid Sunfish, don't use it for bait, save it for the display, they grow big fast and have unique colors.
Don't worry about the mule, just load the cart