I think that a bun that gets used to one dog will have an easier time to get used to other dogs. A ten year old well trained dog sounds pretty much ideal.
I introduced my dog and first bun when the dog was 3 and the bun had just been found in the woods. The bun actually had to ride home in her crate (dog got to ride in the back seat). That crate was of course soaked with the dog’s scent. Bun did fine though. He might have been used to dogs for all I know.
My 2nd bun was young when I found him and had been living feral for a while. He was never fearful of my dog. He wasn’t a fearful type bun. By then my dog was so very used to living with a bun that she was barely interested in him.
I think your method of introduction sounds good. Buns are different from dogs in that buns are far less interested in following commands and they as a rule have very little will to please. So you have a better chance of controlling the dog by teaching it the rabbit is a family member. Most dogs can live happily with cats, but they’ll still chase cats they don’t know. The same goes for buns, a dog will still want to chase wild buns.
Most important imo is to make sure the rabbit can always, if it chooses to, at any time, get away from the dog and go to a place that’s actually safe, meaning a hiding spot where the dog has no access. If the dog is an experienced hunter with a high prey drive it’d still catch the rabbit, but you know dogs so I’m sure your judgement will be sound.