Yeah... I know the can of worms thing.... not sure I want to go down that path really. I have enough on my plate. I do know that if you keep breeding the same line and improve it every season you are making good progress. I saw that in my Marans. I have had them the longest. Rocks second longest.Crossing anything to anything is to start a wild fire of genetics. My word of caution here is that this not a trivial matter. I would strongly suggest that those beginning their Rock breeding career put most of this chatter out of their minds.
Do this instead. Start with hatchery stock and learn husbandry. Then, get a box of eggs or a solid trio or quad of the very best birds you can secure, from a breeder who will tell you the truth about what you're getting.
Breed that quad with the Two Family, spiral system for 5 years. Learn this craft. Bob always said that 90% of the folks will be flash in the pan, here today and gone tomorrow.
Propagation is pretty simple. Breeding quality birds takes a life time of commitment, passion and learning, learning, learning. Keep it simple. Shoot right down the middle. Stay small. Focus on quality. Build relationships with other good breeders. Dare to allow your birds to be exposed to peer review and judging.
Focus on ONE main breed. Very few folks can juggle more than two and do it very well. There just isn't the space, the pens, the money, the time or the patience.
OK, that's me (and a whole lot of Walt, Bob, Bill and other voices in my head) so take it for what you will.