I think you should try the pepered first , what is the leopard ? there are at least 4 species that are called that. they are C. julii, C. sterbai,C. leopardus and C. trillineatus( spelling ).
The leopards are likely to be the last one
The pepered cats are one of the easyest cory's to breed , they prefer it cooler 21C.
Best size tank for breeding is 600x300x300mm, 50lt think.
how to breed, feed them till female is full of eggs ,frozen blood worms works very well , only do very small water changes untill female is full , say 2 weeks. then do a 50% water change droping the temp by 5C so from 21C to 15C OR what ever temp you keep them at. all you need in the tank is a small sponge filter and an air stone . after you drop the temp by 5C TURN THE AIR STONE ON WITH LOTS OF BUBBLES .
If you can not sex them on site then you have young fish or all of one sex as with both pepereds and tri's the female is 1/3 to 50% bigger then the male .
hope this helps