Happy birthday to your LO!
He's had exposure to milk before in foods, right? If so, I don't think it matters when you offer the milk/formula combo. I might do it at both for the consistency. I'd probably try the cup before breakfast , as long as he's still eating breakfast -- has he had a sippy before for other things? As long as he's used to it, he should transition decently to the cup for milk -- it doesn't really matter if you hand it to him or snuggle as he drinks -- eventually it will happen with breakfast but for now I wouldn't worry.