Most milk stout recipes use about 8% lactose (you're a bit low) and I don't see a reason why a "milk ale" would be any different. My only concern would be creating an overly sweet beer. Milk Stout works because of the bitterness of black, chocolate and roasted malts. Here you're piling sweet...
Bootleggers Mint Chocolate Stout. This has been their seasonal offering the past few winters. Tastes like drinking chocolate stout while chewing a wad of winter green gum. Definitely not my cup of tea, but the guys at the brewery say it sells well during the holidays.