Please note I dont have all these fish in my tank, I am merely asking IF I got these would it be overstocked? If yes by how much? And what would you change?
4 female guppys
2 male guppys
2 female plattys
1 male platty
3 glassfish
3 glass catfish or 3 corydoras? (not sure of their acually name)
6 neon tetras.
Its a 60L heated tank
In about 4 weeks after having all those fish in the tank you will be overpopulated with fry. The live bearers will reproduce for their entire lifespan if kept in the same tank as mated pairs. You will need either a second tank or larger tank with an additional option of donating fish to a LFS so that you don't over populate.
I currently have 2 platys who just gave birth to almost 50 fry.
I would consider getting just females as they will get along better and you can buy them pregnant usually. I have Neon Tetras with my Mollies in my bigger tank, they seem to do fine in my hard water but that is because the LFS i bought them from breeds them in harder water.
I recommend something closer to this:
3 female guppys (1.5 - 2.5 inches/5-6cm; males are usually considerably smaller than females)
2 female plattys (Males attain 5 cm (2 inches), females 8 cm (3 inches)
4 Bronze/Green Cory Catfish (2-3 inches) OR 5-6 Panda Cory (Can attain 2 inches, but usually remain smaller at 1.25 to 1.75 inches.)
That would be almost over stocked right there but you could get away with adding some live plants. Using the gallon per inch rule that would be 6 inches of guppies, 6 inches of platys and 8-12 inches of cory...which is about 20-24 inches total in an aprox.15.85 gallon tank which means you don't have too much room. You would be overwhelmed with the amount of fish you suggested.
Even what I suggested is overstocked but again you could get away with some plants.
With the platys you could even try males, but I'm not sure about that (I have only personally ever kept female platys). That would allow you to maybe keep more guppies or one or two more platys if you have males because they are smaller.