You shouldn't need a chiller if you stock accordingly. And perhaps you could put the tank near an air conditioner or vent to keep it from getting too hot?
Orangethroated darters are a bit hard to feed. The only thing mine would eat consistently were TINY guppy fry. Though, they do not need extremely cold temperatures. They are one of the hardier species that can handle warmer temps and less oxygen.
I do, however, NOT suggest the novice catching darters themselves necessarily since they can be hard to I.D. At the least go out, get some pics, post somewhere like NANFA and get the hang of identification before taking any home. Also, those on NANFA will scold you if you start bringing home darters unidentified
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When not in breeding colors various species often look the same, and you could end up with an endagered or vulnerable species without realizing it. Your best bet for darters, as far as legality and ease of feeding is going to be to order captive bred specimens online, that are already used to eating prepared foods, somewhere like jonahsaquarium.com or zimmermansfish.com. You will also have the ability to attain a greater variety of species that you may not be able to find in your area. You can also order blackbanded sunfish online, and they would be quite suitable for your setup, as opposed to the pygmies, which are not true sunfish, and I can tell you from experience are difficult to feed, and as suggested need their own tank.
Even liveaquaria has some natives, such as flagfish, that are easy to keep, do warm temps and will eat algae and anything else you give them.
I'm of course not suggesting you don't also go out and see what you can net! That's part of the fun. If you know your tank is going to get warm in the summer, the best bet would be to go somewhere like ditches, swampy areas, and shallow lakes or ponds that get warm in the summer, since the fish in those areas will be more likely to be able to handle warmer temps, less pristine water, and lower oxygen levels. Whereas if you go to somewhere like a springfed creek, you may find some beautiful specimens, but many of those species may not be suitable for your warm tank. There are also often laws regarding collection in those places, since some of the most vulnerable species live in those type of areas. I know here in missouri you can not collect fish from spring branches without permission, though you can usually collect fish from waterways that they feed.
As far as species, topminnows (a type of killifish) are a good starter fish since they will generally eat whatever hits the top of the water and are very hardy. I'm not sure what other killifish you have up there, but these species in general take to captivity fairly well.
Someone else mentioned madtoms, and these are very hardy, but some can get large enough to eat your small minnow-like fish. Also, don't mistake something like a baby bullhead for a madtom....I only mention this because I have seen quite a few people do it, ending up with a fish that quickly outgrows their tank and eats everything.
Right now I have a little group of blacktail shiners in my tropical planted tank that are doing well, and they survived and grew from fry in my practically unfiltered pond throughout the summer (and it gets near 100 degrees here, sometimes over, therefore the pond even in the shade can get into the 80s).
So there are various species of shiners that can handle warm temps. I'm not that knowledgeable on shiners myself, but I do know some don't do warm less oxygenated water, so try to do your research and stay away from those and you should be fine.