My old "artificial stream" in PVC pipe was a pain in the ass to build, wasn't very cool to observe, and wasn't at all worthwhile. I didn't really know anything about aquaria at the time. I wasn't very successful raising any but the hardiest bugs.
Since then, I haven't tried another invertebrate aquarium, but I have been running a saltwater fish aquarium, which is very involved. That has been very instructive, so I have a much better idea what I'll do next time I set up an invert aquarium.
The first and most important thing would be finding a really good book on freshwater aquarium keeping... maybe more than one. I haven't really looked into what's out there. You should get a basic understanding of nitrogen cycling in a freshwater aquarium, and what you need to keep your ammonia and nitrite levels down. That could determine what substrate you use, among other things.
For water temperature, there are a lot of high-maintenance tricks like Gonzo suggested, or you could keep it against a cool basement wall, near an air conditioner, etc. Otherwise, an
Ice Probe Chiller is probably your best bet. I plan to use one of those next time.
For current, don't worry about creating an artificial-stream-like environment. Just get a little circulation pump like a
Koralia and you'll get all the current you need. I would suggest trying to landscape the aquarium so there are some rocks right in front of the powerhead that get STRONG flow for clingers, and some very sheltered areas elsewhere.
Introduce critters by drip-acclimating them, rather than just dumping them in or simply temperature-acclimating in plastic bags. You can learn how to do that online with a simple piece of aquarium tubing with a knot in it to control the drips.
Lighting is another topic I'll have to study before I try this again. Simple is probably fine, but when I do it I'm going to aim to grow a natural amount of algae on the rocks for grazer insects, and possibly some natural plants. Aquarium stores sell pretty cheap timers you could use to at least mimic a natural day/night cycle.
Hope these things help. You've got me looking forward to trying it again.