I think certainly you can start to move in the direction of using a cup, instead of a bottle, if he's willing. That's really just about trying different cups, offering them and seeing how he takes to them. Though when we did it, we started with the daytime bottles, not the bedtime or overnight bottles, so you may find he's more resistant if the times when he's having them he's tired or not fully awake. You might try him with milk for meals during the day in a cup and see how that goes? If it goes well, perhaps try at bedtime or during the night.
As for cutting out milk altogether, it's recommended that toddlers have about 500 ml of milk a day anyway, which is about 2 full tommee tippee sized beakers if that gives you an idea. So the amount sounds about right. Is it possible to fill him up more before bedtime so he sleeps longer without being hungry? Maybe a snack before his bedtime bottle? We did a small bowl of porridge before bed for a bit, now we just eat dinner later. Or would he go back to sleep without milk and wake ready for it at 6:30/7?
Since he's already only have it twice a day, he's probably right around the amount he ought to be having and I wouldn't be keen to try to cut it down too much more. At 13 months, my daughter had cow's milk 3 times a day (we were just moving to cups during the day with a bottle still for her bedtime one), maybe about 150-210 ml each time, morning when she woke up, mid-afternoon and then bedtime. That dropped to just morning and night most days maybe by 14 months and to just bedtime most days by 15 months. She does have milk still with breakfast most days (in her porridge or cereal or a small bit to drink along with her food) and at nursery, they offer milk at snack times, so she still has it roughly twice a day. It's just with or in food except for the bedtime one, which is 250 ml, adding up to being about 500 ml a day. She's nearly 3 now and still has that. That said, if milk at 5am is working and it means you get enough sleep as opposed to being up and starting the day at 5am, I wouldn't worry about cutting it out right now. Lots of kids wake needing comfort at that hour. Milk is comfort, so are cuddles and sleeping with you, so there are other ways to do it, just depends which works best for your situation and sleep needs.
