I have a 15 gal tank that has just finished cycling, i love cories but i need some help deciding...
1-How many?
Preferablly 6 or more but at least 4 since they are social grouping fish. And 15G is big enough to have them 6 or more. If you have dwarf cory, you can even have 12.
2-What types?
Pretty much open for any corys except Brochi and Super Arcuatus since they get little bigger than rest of the Corydoras. And check the water parameter and hardiness of the species because not all of them have exact ly same water parameter/care requirement.
3-compatability?
Similar sized peaceful middle top leveled fish is ideal tankmate if their water parameter requirement is similar.
4- if i wanted anyother fish or shrimps, what would be best?
I have kept the Corys with small Tetras like Neons, Glowlights and Lemon Tetras and they get along fine. Just make sure the top and middle feeder does not get all the food and cory get some food also.
I also kept hatchetfish with them. And now all the Cory tank have Cherry Red Shrimps and they can coexist. Although I am not so sure about the shrimplets since they are not much bigger than baby brine shrimps. And I'm sure the cory would eat BBS. So I usually move the mother shrimp with eggs to my other tank before the shrimp hatch. Then again, they multiply fast enough, they are spreading to many tanks. I also have some pleco such as oto and bristlenose with cory so far they are fine although my bristlenose is still half their adult size and some grow up to do. But I read they should be fine as long as give them enough space and hiding spots for all.
And please make sure the tank is properly cycled before add some group of fish. Most of the corys are peaceful interesting fish and they would make good tankmate for other similar sized peaceful fish.