On the "space" concern in the smaller quarantine tank--not an issue. The fish will be small as I previously said, and for a few weeks it will not be an issue. However, make sure you have floating plants, covering the surface. Water Sprite, Frogbit, Water Lettuce, Salvinia, a stem plant like Pennywort--whatever. Even duckweed if that is all you can get. This has a crucial role, first it shades the tank and the fish will be more "comfortable" which means less chance of ich, and the floating plants will gobble up ammonia as fast as the fish could ever produce it, even if you overstocked the tank ten times.
As for the 55g, you need floating plants here too. The fish mentioned all need this, they are forest dwellers and that means no bright overhead light. It really does make a significant difference (benefit). Stocking is fine, whichever. Just add all of the intended number of a species at the same time. Example, all 14 neons together, then all panda cories together (try to get the entire number if you can).
As for the 55g, you need floating plants here too. The fish mentioned all need this, they are forest dwellers and that means no bright overhead light. It really does make a significant difference (benefit). Stocking is fine, whichever. Just add all of the intended number of a species at the same time. Example, all 14 neons together, then all panda cories together (try to get the entire number if you can).