New Sterbai Corydoras
 

Got some new Sterbai Cory's recently, which means I have 3 in total. I now have 13 fish in my 10 Gallon. Do any of you think that is too many?

Your neons don't count much as far as what they contribute to your bioload.
Your cory needed to have some buds of his own so it's good you got him some company. Not sure I'd anything else to your tank, though.
Also, you can't say how many fish should be in a 10gl, as it all depends on WHAT species of fish you are talking about.

Agreed. You could put about 1/10th of an oscar in a 10g, but maybe two dozen microrasboras. Depends on the fish.

Your corydoras would really appreciate more of its own kind. You could probably get away with adding two more and you'd have a pretty heavily stocked tank but so long as you kept up with water changes (or even added some plants) you'd probably be ok.