Re: Stocking questions for a 55g tank
I would get a few more female platies, as your single girl will be unhappy without company. Just be very careful sexing them if you don't want fry.
I also agree that the corydoras are best in groups, the larger the better. They are also much more fun to watch in huge groups, as they swarm around and are extremely social and playful. I love the panda cories myself, because the marks around their eyes do make them look like playful little pandas or raccoons.
The larger the group of neons, the more brilliant the tank will look. There are tools on site, I think, that can help you ensure you are not overstocking your tank.
joy to the fishes in the deep blue sea
55, 30, 30, 20, 10, and 10-gal. freshwater tropical tanks