I've bred corn snakes and failed to breed ball pythons. So IMO it is easier to breed corns. YMMV.
IMO, if the ultimate goal is to bred retic pythons, starting with corns would be a bad choice. Because corns are temperate zone snakes, with different breeding requirements. You would probably learn more that is applicable to retics from starting with ball pythons.
You might find some of the Australian pythons both more interesting and a more manageable size than even super dwarf retics. Womas, water pythons, spotted pythons, carpets, etc.
Others have covered the downside of breeding better than I can. For what it's worth, culling is necessary, but it is emotionally difficult for me. And for many other breeders, as far as I can tell. Be prepared.