This raises a couple important issues, both concerning numbers.
As I frequently write, many of us get hung up on numbers vs tank size. While one does not want to have more fish than the tank's biological system can support, this is not the real issue nor is it even the primary issue. If we choose species "x" we are obligated to ensure it is going to have what it needs to be stress-free. Stress is the cause of over 90% of all aquarium fish disease issues. So avoiding it is crucial to fish's well-being and health. If species "x" needs a group, it must be provided with a group. If this exceeds the tank's biological capability, then don't get species "x" but something else.
That brings me to the second numbers issue. Shoaling/schooling fish need a group of their own species. This is a mandatory need, they expect to be in a group, they depend upon the group for security which means a lot less stress. Some species also have hierarchy needs, others have interactive behaviours that to the fish are critical to survival, and these have to be considered too. All shoaling/schooling species will always be healthier with 10 or more than they will with five or six. There are scientific studies now proving this, though many of us have recognized it for years. This is part of the genetic makeup of each species. It applies to all characins (tetras, pencilfish, hatchetfish), many catfish (cories for example), all rasboras, barbs, danios, loaches, rainbowfishes, and some others.
You have 10 black neons, so they should be well adjusted. Any shoaling/schooling fish you acquire will need 10-12 minimum. Panda cories are mentioned, so a group of 10+ is needed. You can mix cory species, they all chum around together, though it is still a good idea to have a few of each species. I have had these fish for more than 20 years, and several species because of being unable to buy more than sometimes one or two, or three of certain species, but it was very obvious that those who had five or six of their own did like to spend time together, or in smaller numbered groups of their own, while also socializing well at other times in groups of two or three different species. I would recommend five or six of each species, with two or three species, or all the same...point is, that 12-15 even 20 is a doable number here.
