I currently have my 75 set up as a native fish tank, with some different species of sunfish. They are a LOT like keeping cichlids behavior wise. Just dont get too many because they are very territorial. They also have some AWESOME looking colors depending on which species you get. I have 4 Warmouth sunfish in mine, which almost look like mini largemouth bass, and have the biggest mouths out of all the freshwater sunfish. They are dirty fish, similar to goldfish, so have a good filtration system.
Also the hardest part is getting ahold of whatever species of sunfish you want, that is if it isnt native to you. I can put you in contact with a guy i know that breeds warmouth. I ended up catching mine in a local lake, but its up to you.
Another hard thing, especially if wild caught, is getting them to eat. Mine started eating after about 3 days of adjusting to the "aquarium life".
Feeder fish work well, as that is a natural forage. Rosy reds or comet goldfish work well. Night crawlers are also good, but you might have to cut them up if the fish cant eat one whole. I ended up getting warmouth due to the fact they have bigger mouths so the option for food was a bit more broad. Bluegill have smaller mouths so options are a little more limited, might have to cut the worms up for bluegill. Also another option is frozen crawfish. Thats what i use. They sell it at my local walmart in the frozen seafood section. Its 7 bucks for a "frozen slab" of it. I have a mini fridge in the "fish room" that i keep it in. If you need to defrost it faster you can keep it in a plastic container and nuke it in the microwave for about a minute. It lasts a good while, but i usually get 4 or 5 packs of it to stock up for a while. My warmouth go INSANE for the frozen crawfish, its like crack for them. Only bad thing is that it can dirty the water up a bit, so water changes are essential, but they are dirty fish so you should be keeping on top of it regardless. I have two HOB filters each rated for 90 gallon tanks, which is overkill but it works very well.
Also a lot of people dont mention this about sunfish, but they have very cool personalities! Mine beg for food, i say they are "freshwater dogs" because thats exactly what they act like. After they get used to you, they WILL beg you for food. I can always tell when mine are hungry. They are always happy to see me as well. I actually have them next to a tv in the room. If you sit in the room and watch tv, they also watch tv with you!! Its like they understand whats going on. They are also very smart fish, and are VERY aware of their surroundings. They notice me when i just pass by the room while walking in the hall.
EDIT: Forgot to mention. If you go the sunfish route, make sure have caution when adding any live plants if the fish are at adult size. They will sometimes eat plants as a snack. You CAN add live plants, but make sure the plant is big enough to where if they do take a bite or two the plant can still be fine. If you decide to put some plants, id only put in a few and see if they fish mess with them. If the fish havent messed with them after about a month or so, then you should be okay. I had plants in my 75, until i didnt. The plant got pretty big and one day the fish decided it was in their way so they tore it up and ate 80% of it. I ended up giving up on plants and just added plenty of hardscape. Frogbit worked well for me, but they still do snack on it. It replicates so fast that they dont really make a dent in it though. These fish are ambush predators, they will appreciate some hidey holes.