Sedaeng, You may keep your roo or use a superior roo. Any hatchery will not give you a better rooster, therefore if you want to improve the looks of your flock closer to show quality, using a show quality rooster from a DCA breeder will get you there faster, because you can mate the resulting daughters and grand-daughters back to the good roo. Some inbreeding is ok, especially following an outcross, you don't want to do this year after year forever. Line breeding is considered better than brother-sister. Line breeding is putting the son-daughter with the mother-father.
On outcrossing - outcrossing many times produce a larger bird than the parents. therefore, do not use a bird which is above weight for the standard. Cocks should be no more than 7 lbs, cockerels 6 lbs, hens 5 lbs, pullets 4 lbs.. Weigh your birds! Dominiques are not supposed to be as big as a Plymouth Barred Rock or Rhode Island Red. Compared to a Buckeye, a Dominique looks almost runty.
You can cull early for wry tails, crooked combs, crooked toes. Do not cull for plumage, eye color, or size until about 6-7 months. Most of the males may be ready for eval by 6 months, not before. You will see an 8 month old blossom out beautifully when you were sure he would be dinner.
Breeding Dominiques to standard is time consuming, costly and requires space to divide your growing boys away from the layer flock. They can be raised together as long as they have no girls to compete for. Keep young pullets with the main flock as long as you have peaceful hens, not mean girls.
I usually bring my youngsters outside at 5 weeks if it is warm, in a fenced area alongside my flock. At around 8 weeks I begin to assimilate them into the flock in the evenings, allowing them out into the main yard with them as they are getting ready to go to bed, each night giving them more time. Then I begin carrying them into the main coop at nightfall and putting them on their own low roost. By 16 weeks I remove the boys away from the adults. They start to annoy the hens at this point. If there are broodies with chicks, I may do this earlier. Last year I was able to cull down to two cockerels from 25, and 3 pullets from 18. You do not need a whole coopful of hens to produce the next years' batch. But I am a minimalist. I keep ONLY breeders and maybe one or two extras of each sex, never more. I don't like running out of space when I want to bring in the next year's batch. The only individuals that get to stay are those who are closer to the goal than the previous gen. I have a few "pets" who are there to lay eggs for the table, but everyone else knows they have a job to do. The cocks take their role very seriously
This is the fastest way to improve. IMO