I would just offer him the same amount in cow's milk and at the same time as he's been having formula. As for meals, I would feed him whenever you normally eat meals and if he's hungry in between, offer small, healthy snacks, but not so much that he will still be full at mealtimes. At meals, I'd offer him as much as he's hungry for, as long as it's healthy.
My daughter is 15 months, so a bit older, but her meals have been the same since 12 months.
8am - breakfast (bowl of porridge and a banana)
12pm - lunch (cheese and onion sandwich, some puffs)
2-4pm - snack (rice cakes, oatcakes, blueberries, etc. sometimes with milk)
5:30pm - dinner (baked beans with cheese, some peanut butter)
7pm - milk before bed
The only thing that was different at 12 months was that she was also having milk when she first woke up and then in the afternoon around 2pm (sometimes instead of a snack).
Basically, think about when you eat, 3 meals a day and then you probably nibble or have a cup of tea or coffee or whatever in between. If he's genuinely hungry and it's good, healthy food, you can't overfeed him.
