I have an employee who breeds a few species of darts. He's a busy man with a full time+ job, works for me a day a week, pretty much runs a zoo in his free time, and has a wife and two kids under 4 so isn't going to hold your hand through the learning process, but if he has a species you want I'll put you in touch.
My gut feeling as a guy who "knows you" and has kept some dart frogs is -hold off for now. They require a LOT of attention, and so does their food. Half of the work is your Drosophila cultures and such. You have multiple aquariums and it's only natural to want "more." But it might be a good idea to dial in what you have and get things healthy, growing, propagating, breeding, and focus on that rather than try to acquire what strikes your fancy on a regular basis. As a man over 50 who has lived with glass boxes full of life in his house since he was your age I say this with upmost admiration for your enthusiasm. But I have seen time and again SO many enthusiastic hobbyists drop our hobby completely from tying themselves to all the time, money and energy required to keep more than they can stay on top of.
If you are really feeling keeping amphibians, try a hardy salamander or newt, I'll direct you easier species. And aquatic ones might be right up your alley! If you really want to try a dart, set up the enclosure first and get a couple of captive bred Dendrobates auratus at a reptile show and see if their care is something you want to be married to.
Nothing good happens fast in an ecosystem.