Stocking for 20 gallon long...

[Chazeman2]

I'm planning on starting a 20 gallon long cory tank. I was considering doing some corydoras sterbai and panda corys. How many of each would I keep?

[Corycory]

How long and how wide is the tank?
Normally minimum 6 of each cory type is preferable to keep them happy. The bigger the footprint, the better for corys. How many depends also on your filtration and flow, make sure it's more than enough to provide enough flow to keep the sand clean without debris gathering(presuming you'll put sand as it's best for corys)

[Chazeman2]

The dimensions are 30x12.i have sand ordered and a filter thats is rated for 155 gallons an hour.

[MChambers]

I think you could have about 10 corydoras in a tank that size, but others may recommend fewer.

I would think carefully about whether you want to have those two types in one tank. Sterbai like warmer temperatures, while pandas like cooler. I think they both do okay at about 75F, but that's on the low end for Sterbai and on the high end for pandas.

[Corycory]

I agree with the above comment, maybe replace the sterbai with different species as most prefer it cooler, it will save you on heating the tank too as depending on room temperature the heater won't work that much.
I think you can fit the corys in, the only suggestion I would have is put some branches/driftwood positioned higher up in the tank, something like tree with branches, anubias, java fern and java moss attached would be great and you need no special care for them. Corys love exploring all levels of the tank but most tanks have the decor too low and they have nowhere to go bar the substrate. This way it will keep them happier, you will utilize all the tank and you'll see them all over the place rather than bunched together on the bottom, bored to death.
Here is a picture of one of my albinos for inspiration