
First thing with an OES: Has he been hipscored and does he have an acceptable low score. Also has he had any other relevent health checks? Is he KC Reg? Has the bitch also had these things done?
Do you have trust in the bitch owner that they have the welfare of the puppies at heart & can ensure good homes for your boy's puppies? You wouldn't want them to end up in rescue (or worse) would you?
Are you a member of a breed club & do you have enough knowledge of the breed to be able to assess whether the 2 dogs are both good examples of the breed with excellent temperaments and are a good match? What do you know about the pedigree of both dogs? If the breeder of your boy was a responsible breeder, your first step is to contact them.
There is a lot more to breeding than putting 2 dogs together & a lot of work & research to be done beforehand if you are going to do it responsibly.
If you can answer yes to all the above, why don't you join, then you can ask as many questions as you like.
If your answer is no, don't be afraid to refuse a stud for your boy - it's your decision.