I know you want a fresh water tank with tropicals but that tank is sreaming out to me to be a nano marine tank with zoanthids and maybe a pair of clown fish. Zoas come in amazing colours, and clown fish really are active little guys. Even a seahorse or two would go great in a zoanthid tank with some branched hard corals for the sheahorses to cling to.
But that is just something I would do
Going with tropical fish then you wont need the live sand or live rock.
Fish wise (but please read the topics on cycling a tank prior to getting fish) the length of the tank is going to be the limiting factor.
A single male fighter would go well in there as long as the filter wont be to harsh and blow him all over the tank. Even a nice little soriety of female fighters would work and the bonus of them is you can get a real rainbow of colours within the one species of fish.
Cardinal tetras will work with a fighter but some fighters wont tolerate tank mates of any type and many cardinal and neon tetras have reduced health and vitality thanks to mass commercial breeding. My advice with just starting out is avoid tetras, especially in a new tank that will more than likely hit a few hurdles.
Its not a huge tank with lots of length so I would try to avoid fish that want a good sprint the length of the tank.
And please don't put a turtle in the tank with fish
, they really are not a good combination with the turtle needing certain lighting for healthy shell growth and needing a place to haul out and bask. Plus the turtle will more than like see any fish tank mates as food, and turtles are messy needing frequent water changes due to their usually high protien diet.
That tank would also lend itself well to being a fresh water shrimp tank, depending on what country you are in will determine what fresh water shrimp are available to you, but WOW there are some beautiful shrimp being kept and bred now.
