Hi! Sounds like you have been given some great advice here. Here's my two cents:
We have 3 tiny OEGB hens with 1 OEGB roo in with 81 PRIR (15 cockerels) and a huge Partridge Cochin cockerel. For us, this situation works.
The OEGB hens do get bullied occasionally by the much larger and more active fowl as the banty girls seem to be more passive in their nature. However, those bantys run circles around the PRIR except at treat time (lol), and can escape into tiny spaces to get away, and also fly very well upwards without much prep time, unlike PRIR or the Cochin cockerel, who is a completely docile marshmellow, and hasn't even pecked anyone else.
The tiny OEGB roo (1 lb who thinks he's 10 lbs) is top bird of the flock (go figure. lol), and he is gentlemanly and protective of his tiny girls, chasing away the PRIR cockerels who try to mate the Tiny sisters occasionally. Even though once an 8 lb cockerel has jumped on the back of a 10 oz banty hen, the Banty roo knocked them off by running up and chest bumping them off, then giving chase, so, we haven't had any of the hens obviously damaged, just a few pecks to their combs and neck feathers missing.
In your situation, I might consider getting some more standard sized hens that he can mate, and perhaps at least another little banty pullet friend for her so she isn't the only banty to lessen any bullying to her. Our Banty girls hang around together all the time, but they have two other PRIR hens that makes up Banty's harem as well. This smaller subgroup seems happy about this arrangement, and even sleep together on the roost. Banty roo is also protective about his much larger red girls as well. The only real issue I've watched for these days is eating... the PRIR graze like land piranas, and bantys take their time to eat, so they can get pushed out of eating huddles for treats. So we always try to check craws to make sure everyone has had enough.
But, please make sure you quarantine any new birds for a few weeks in a separate area before putting them all together for health precautions.