Hi Ollie
I am currently in the process of doing much the same thing, although I have cheated with the plants and used tropical species. My tank is room temperature and I keep minnows, sticklebacks, bullheads, loaches, newts, crayfish, caddisfly lavae, freshwater shrimps etc. The beauty of this type of setup is that you have access to the whole ecosystem in any river so can go beyond just fish and plants.
I have had no luck with either rainbow or brown trout. But have not tried since I have managed to stabilise the conditions and create a real river flow using pumps. I get the feeling it wouldn't work though. Crayfish are great fun, but if they get too big they really stir up the substrate. You can't rerelease them if they are american crayfish cos they are an invasive species but you can eat them.
Minnows are so active and interesting, especially if you have a good flow moving through the tank.
Sticklebacks... The male goes red, builds a nest in spring (a tunnel of twigs) and dances around it to attract the females. The female lays her eggs and leaves the male to protect the brood, which he will do fiercly. You will see a little shoal of tiddlers coming out of the nest and being chased back by the dad.
Caddisfly lavae build a tubular shell from what ever material is available, usually twigs or gravel.
Newts are awesome but will need some land too. Sadly mine got eaten by my Mynah bird. That's the trouble with nature it's always eating itself. With a tank the size of yours you could have frogs and toads too. Dragonfly lavae are great, but will eat the small fish, it's worth it to watch them hatch and to have a beautiful dragonfly drying itself on a reed.
Best of all is catching the fish. For my 32nd birthday I had a biology field trip themed picnic. Nets jam jars and pack lunches.
Best of luck. The whole thing is so fascinating.
Rufus
Keep it real.