I would either get rid of one species of cory and add to the school of the leftover species or add 1 peppered and one bronze. They need schools of at least 3.
I would personally leave out the platys. I think that a sunburst and a wagtail would look out of place.
The black tetras would look fine with the cardinals.
If you dont mind selling/trading fish then this is how I would stock it:
7 Black Tetras - 15.4 inches
5 Bronze Corydoras - 15 inches
10 Cardinal Tetras - 17.5 inches
All of those fish will follow the
inch per gallon rule well so you will have 47.9 inches in your 50 gallon. It is always good to go a few inches under. Reason being is decor takes up gallons and it keeps your water readings lower since you have less
ammonia which gives you an overall healthier fish tank.
Thats how I would stock it and really with a 50 gallon tank you should keep it a few inches below 50" not 55" as Dave said. 55" would actually be close to overstocking your tank.
Hope that helps.