Just to add my 2 pence (Cents) worth.
I think the very first consideration is what species you intend keeping and plan the tank set up to suit.
The term 'Corys' may be a standard one but their natural habitat conditions are not.
Substrates may vary slightly, but for most there will be a fine sand underneath them, this may have a smattering of leaf litter, none at all, or a dense layer. I collected C. delfax in a tributary of the Rio Mammon in July 2011, where the leaf litter was 10" - 12"deep, under which was very fine white sand. the water parameters were, pH 4.8, TDS 8.3ppm, temperature 76ºF.
There are many members here that have collected corys from various locations and I am sure once you have decided on the species you want to keep, they will be more than willing to help with habitat information.