Ppl usually say LOs can be ready for a Gro clock / lights on timer from around 18 mo, some slightly later, so maybe wait a few weeks and then give it a go. I introduced one with L at about 19 mo (iirc) and it worked v well.
No, at this age I wouldn't offer milk at 4am. However, if you're worried he could be hungry, maybe think about what you give him for dinner. I'm sure some foods are more sustaining (fattier foods, some carbs , or protein, but I'm not sure what exactly ..) than others. I'm not really sure what they are though tbh but I think I have read ppl recommend some foods over others. Perhaps post on eating for toddlers for advice about which foods are good for sustaining a LO overnight. How long has it been since he's not been feeding at night?