If you want to bred top quality Marans, get show quality and cull heavily. My first BCM was decent, then I ran into a great breeder (Cindy) who taught me tons....based on what I learned from her, I sold most of my first flock. She gave me a screaming deal on top hens and roo to get me started. Then she taught me some more.
Out of 40 or so chicks hatched this year, about half went as pets (sold them as crossbreeds so people would not use them as breeders)
Then I grew out the hopefuls and about 10 made the grade. Sold most to people for their first flock, thus doing the same as Cindy had done for me. Kept one hen and she turned out to be outstanding.
Now I have a super nice roo that I just bought, two hens still left from Cindy, three from LP lines and my one that I bred. Running into Cindy who spent time educating me was a wonderful and best advice I ever got.
Get a mentor. It is the best you can do for your program. Cindy doesn't know this yet but she is getting some Legbars, Rhodebar, Isbars or Spitz pair as a gift for her kindness...her choice. She didn't have to help me but I sure appreciate that she did. I learned a lot and still learning lots.
The hardest part was looking at my flock with a tough eye on culling. If I wanted a flock just for eggs, I would have kept more. But I wanted a flock to bred for the standard as well as egg color of 4 or more. Right now I am at 4-7 range. I also bought eggs from top breeders to add to the flock.
Find a mentor and ask question. Be sure to thank the mentor as well. Be tough on your breeding. Be open for suggestions. Don't take offense if the mentor says your hen/roo doesn't make the grade. Pay the price for top quality stock. Start small. Pick one or two type to go for (I chose BCM and Wheaten) but no more as then it can get too confusing.
You will find there is NOT a perfect hen or roo so you need to find what fault you can live with and hopefully bred out.
