I have never seen the medaka's for sale anywhere around here, is why I had to ask. Yes, they would be a perfect fish for a small tank... but also... I can already hear a lot of customers complaining that they aren't "pretty" due to their sort of bland coloration. If color isn't an issue, male feeder guppys would be the absolute best inhabitant for such a small tank... not needing much of anything to thrive, and still a bit of color.
As for the white clouds, even in larger tanks, I've always seen them sort of "hang out" in small groups, 3 - 5 in an average group, not the type of "pacing" or "overactive" habits that many stream fishes exhibit. I've always had great luck with them in small tanks in a group of 3, as have many of my customers.
The expense of the galaxy's would be a bit much for most people. Here they now sell for $10.99 each (down from the $13.99 they started out at), though they do seem to be rather abundant. Another problem with the galaxy's is that they jump a lot. I have already lost 6 of them when they decided to go tank hopping in my fish room. I started out with 7 (yes, I spent the money when they first showed up in the store here), and I found out where they went when I spotted the last one swimming in the tank down below, home to my 6 inch red tail shark. I have to assume he ate the others because I never found bodies anywhere. I rescued the last one, but recently lost it when it jumped out of the tank during the night. Like bettas, they seem to get through the smallest of places. Yes, my tanks were covered, and they were done so as tightly as possible. That was an awful expensive lesson learned. Those fish had a 55 gallon tank to themselves, only other tankmates were ram's horn snails and ghost shrimp, and the tank was planted so thickly, it was hard to find the fish. Just a note: The galaxy rasbora was found to actually belong to the family of danios, and has been renamed "celestial pearl danio". The scientific name has also changed from Microrasbora sp. to Celestichthys margaritatus. After having done a lot of research on what little is known about them, and having kept them for almost a year before the "accident", I would not suggest mixing them with any other danio species, and I also would not mix them with any real active fishes. Good tankmates for them would be black phantom tetras, lemon tetras, neons. While they're a beautiful fish, they're not so easy to keep.