
You may very well be in the right of it, and be entitled to have the endorsements lifted, but I would think about it.
Breeding requires knowledge, and as you say we all have to start somewhere and at the start we rely on the knowledge of others, especially the breeder of our foundation bitch, and the owner of her sire.
They are the ones who should know why they combined those bloodlines and what god and bad things the line has to offer to help you with the direction to take yourself.
The fact the breeder bothered to put endorsements in place was a good thing as it showed that at the time they did at least care to protect the pups and breeds best interests.
The fact that they now do not seem to want contact (did you make it clear who you are or just ask to friend them, they may like me not like to friend people unless close to them), may mean they were not that interested in continuing their interest in the breed beyond that one litter, not the best basis for you to breed on.
What steps have you taken to educate yourself about yoru bitches bloodlines? Are you in contact with breeders of dogs in her pedigree as mentors? Do you belong to the breed club, have attended educational events about the breed and shown and/or worked your bitch.
As others have said your leaving things somewhat late. It is generally advised in medium to large breeds that a bitch has her first litter before 5 years of age.
Think seriously, if you have not down the serious groundwork learning about the breed and bloodlines you may be better off doing this now, showing your bitch etc, and then look around for a breeder whose stock you admire make friends within the breed and buy in a potential foundation bitch. This will be a better start and may lead to success sooner than trying to breed up from a very average bitch over several generations.
I started off with a bitch of excellent bloodlines, with a champion litter brother, and it took me three generations to get a top class bitch to keep, though a RCC winner from second homebred generation. Generally the better you start with the sooner you will have success as a breeder yourself.