You've got a good a pair to start with. Good shape and pattern. They'll take about another year to get to their full size. Keep them on a good balanced feed with a little extra protein, they'll need it. I add oats and sunflower seeds to the feed for my Orpingtons and Brahmas for extra protein and fat.
Leakage is something every breeder deals with from time to time. Even in old established bloodlines deal with it. I myself have used birds with leakage for breeders. Sometimes they pass it on and sometimes they don't. I would suggest trying them out and see what happens. Keep back the birds that don't show any leakage of course. And cull or sell the ones that do get it. Also you might look for another pair "preferably unrelated to yours" and split yours up. Meaning roosterA with henB and roosterB with henA. This will strengthen your bloodline and hopefully help to eliminate leakage problems.
Pattern is one of the easiest traits to control. You want to look for good type to breed with. Meaning the overall shape and carriage, head shape, comb shape, wide set and heavy legs, tail shape and carriage. You don't want to pick up every bird that has good pattern. Introducing a "bad" physical trait will set back your breeding program years to breed it back out again.
Also I would mention, from my own years of experience with English Orpingtons. They are very prone to bumble foot. Keep their bedding clean, soft, and deep "like 2-3 inches" and low roosts so that they don't have to jump down very far. Mine are only about 18-20 inches off the ground.
