Louie and our cat get along great.
They are the best of friends. We do have to keep the cat's food away from Louie. We got our cat when he was very young from our local humane society. Not only did I save a life, but the kittens usually already have their first shots and if they are not already spayed or neutered you can get a voucher to have it done for free. Atleast around here. I don't know about your dog starting to mark, but you do have to be careful of cats marking when they get to that age. Louie does have to be supervised if he is running around free becuase he will get into the litter box, yuck!!! Good luck with whatever you decide.