Well you always want to understock the tank slightly, because if you have the max or a full tank, there is no room left to add the new fish for screening.This could lead to stress do to overcrowding, the filter may not like the new bio-load as well.
Danios , I wouldn't go for, the space is too small. They like to swim all around. Sure you can keep them, but I wouldn't.
I would choose pearl danios. They are so nice looking for a danio. I dont think more than 5 or 6.
I usually leave a few ottos in my 10 for the tank to stay cycled, after my new fish pass. Also have my 2 little baby cories in there all the time, and a few guppy babys , which I give away after I get a new batch of little guys.