Yes, at that hardness, the only tetras I would risk in an 80l tank would be x-ray (pristella) tetras.
Most livebearers will be fine at that, look at the "different" ones like limia and goodied as they don't breed as much as the more common ones.
Don't get swordtails or mollies as they will get too big for the tank.
American/Florida flagfish would be ok, but they do tend to wreck plants as they're basically vegetarian.
Cherry barbs would be ok, most rasbora do better at lower hardness, but you may get away with harlequins, depending on what water they've been raised in.
Rainbow fish, well the smaller ones, would be worth looking at - gertrudae and furcatus are small and pretty and come from hardwater areas.
For the bottom, dwarf anchor catfish would be ok, they like to be in a group and their behaviour is interesting, even if their colours are a bit dull, or you could go for neocaradina shrimp (like cherry red) who are even more interesting and colourful. All the fish would need to be small though so the shrimp wouldn't get eaten.
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& welcome to 
