Goats can be pushy regardless, they aren't usually mean. If they anticipate grain coming at a certain time of day they will yell all day until they get it. They are always looking for an opportunity.
I will just give you a general rule of feeding for a large breed goat. I would ask how much the breeder is feeding and use that as your starting guide.
The first week 8-10 ounces 3 times a day
Week 2-4 10 ounces 3 times a day
Week 5-9 weeks work up to 20 ounces 2 times a day
Start weaning by cutting down on the amount in the bottle
I always have followed up the milk bottle with some warm water, the older they get the more water I give, by weaning I start giving one feeding as just water and eventually both bottles are water, they should eat more other stuff as milk decreases.
If you are using a milk replacer make sure it's for goats, I use Advance Kid replacer, it's made out of goat milk. You can Google it to see if you can find it. It's easy to mix, I add the replacer in a 2 quart container, add warm water, shake, and fill my bottles, I refrigerate the extra, to reheat I put it in the bottles, put the bottles in a bucket of hot water and they warm up quickly, in about 5-10 minutes. I use the screw on nipples that go on measured bottles or on plastic pop bottles.