Sorry, Cadeau, we seem to be getting a little chatty again right now.
I know you are excited about having such a fabulous breed, but these are too many questions to answer in one post! I have to keep toggling back and forth to try and get them all!
I am in no means an expert, but this is what I would do.....
First off, the reason Marans are different from all the other birds is EGG COLOR. That must be preserved.
So I would go for egg color, before leg feathering.
Middle toe feathering is a no no. If he is perfect in all the other aspects, keep him for a breeder, and try against one with poor leg feathers.
Both hen and roo contribute to egg color.
I, personally, would not introduce another breed. This is where we got the comb issues.
The combs seem to be a big problem, I would not keep any of them with carnation, or side sprigs. They will bite you in the butt later on.
Remember, just my own opinions. I am sure you will get many different ones.
Roberta