Hi One_Trick_Pony
How exciting it must be to see so many different corys, all in the same lfs!
If you follow the "inch per gallon," guideline, you won't go wrong when it comes to stocking. In addition to corys, of course you will have to consider the other fish in the tank.
You cannot have too many different corys together since, while they like to spend some time with their own kind, they are comfortable in big schools of any mixture. My 55 gallon tank has only corys except for a weather loach, two gouramis and a couple of otos. They are doing just fine.
All corys get along well together, but I find that if they are similar in size they do best, although this is a pretty loose rule. Pandas, especially, seem to do best by themselves or with the pygmy species.
Keep in mind that if you want to try your luck at breeding any of these, you should get two males to each female, or better still, at least two of each gender. Six is an ideal group to get.
Have fun, and let us know what you decide to get.