You only want to line breed in a controlled manner. So you want to know the paternity of the two birds in question. So the rooster is a wheaten? hen is black? chances are they are not related closely. So it is safe to assume you can start line breeding these two birds for a hobby purpose. The hen is the one that decides the sex of the chicks. So any problems you would hypothetically have if this was a ie; black to black brother/sister breeding of known parentage, you could potentially get more faults, decreased egg production, loose fertility, loose hatchablility, and chick vigor. You have to line breed very carefully, and keep inpeccable records.
So basically I am saying from a backyard flock perspective you are going to be fine with your current genetics, and shouldn't have to add more. Now if you want to know beyond that, that is a whole other conversation. If you are only looking to make replacement birds for your own flock or sell a couple of chicks as easter eggers on the side you will be fine with what you have for a couple of years.
I always encourage people if possible to have some SOP birds in there flock.