Corydoras pygmaes mix well with all types of fish within reason, They just go about there stuff, They rarely each small plants like your HC unless they get real hungry. You can feed them a wide diet too, live dried flake vegies. Its a very easy fish to keep and not too fussy on water parameters either. Just caution with the males, as usual they can get grumpy with the own type, If you wanna sex them just look from above,the females will be larger and more rounded in body shape.
I hope this helped a little.