You're clearly going about this as thoughtfully as you can, and it is a tricky thing to balance what you love and all the conflicting info out there.
Go have a look at zebra danios in a bigger school in a bigger tank, if you can. Or look for YouTube videos of danios schooling. Happy Danios are like a pack of teenagers on skateboards.
The conversation people are trying to have here is the difference between surviving and thriving. Your friends' are surviving, but danios don't thrive unless they have enough space and company to be real party animals.
The other glow fish are a type of tetra that's also not at it's best in a tank this size.
It sounds like you love bright colors. What about some female bettas? Or just a big school of neons?
Honestly I think the best suggestion so far was the one for some male guppies. Or neons and a betta understanding there may be problems.
My bettas also only hide in a tank that size with so much open space. They're most interesting in something densely decorated, but then you run into the issue of plastic plants tearing their fins ...
It's tough and there's no one right answer. I think you'll also find the most reputable fish sites say danios need more space. Check seriously fish, and aquadvisor.
Sent from my iPhone with three hands tied behind my back.