Not sure if anyone has any multiplay plans yet but I've been breeding from some good dogs for a few seasons now and have won several competitions with homebreds.
What I tend to do is only retain dogs in the breeding kennel that have won comps. themselves (not just open races). As you have probably seen, these dogs have a gold cup icon beside there name. I've found the degree of success appears to be greater if you only use comp. winners for breeding but you could hit lucky with other prolific winners !
Like for like distance breeding is a good ploy, but if you deliberately want to breed a pup for a specific distance, say 625m, then breed a 675m to a 475 animal. (combined total = 1250m divided by 2 to get pups potential average = 625m).
Hope it helps with the breeding !