Nice fish choices, very cool. I've never been able to actually find a female dario dario, good work! Every time some store says they have one it's ended up being a stressed out / colorless male. Heads up, though, they will eat baby shrimp and I've never had much luck getting them to eat flake. Also, oto's appreciate the company of other oto's. They'll be alright without but I've had one pal around with a group of cory cats for company before =)
You are totally on point with this. It's called a High Dynamic Range or HDR photo. This is how I did my FTS for my paludarium. It helps to have some photographic experience and also knowledge of photoshop, but anyone can do it with the right tools and patience.That's looking great!
It's hard to capture subtle differences in light and dark with a camera because the camera over-accentuates the shadow and glare. I have a hard time getting good pictures of my riparium setups for this reason; even though it looks great in person, the underwater area often looks like a dark shadow while the foliage closer to the lights often has white blowout.
If you want to get a real good FTS you might try to make a layered image by putting your camera on a tripod and shooting the same shot with several different exposures. You can then stitch them together with Photoshop to get a more balanced image.