A word about castration.... knife is best, as you know for certain you have gotten both testicles completely as you eyeball both of them on the ground. Younger is better.
Check to ensure they actually have both descended before you castrate. Banding is fine, IF the person doing it is very careful to ensure that both testicles are truly descended and below the band.
I have had calves that failed to have testicle descend, so vet had to go fish and get it. I have had calves that someone else banded and he failed to get one testicle below the band. Both cases will lead to an infertile but still dangerous 'bull' rather than a less dangerous steer.
By having clean water available in pen as well as fresh calf starter/grower feed, you can get calves weaned as soon as they consume two pounds of starter a day. I put fresh out every day and feed whatever they leave to other stock. I start mine at a few days old as they are wanting that bottle and I feed some feed by hand to get them the idea that it is OK to eat. Calves that are raised on momma will start eating feed with her at less than a week old.
Unless it is bitter cold weather, I wean off milk at about 60 days. If it is cold or calf seems to be a bit less than I want, then I continue one bottle a day for another 30 days.
If it is bitter cold, then calf coat is a good thing. A calf with momma can sidle up any time to get a full belly of warming milk. A bottle calf can not. Also reason I keep my bottle babies in the barn when it rains until they are three or four months old. Mine ran with my goats, who HATE rain, so they would all run for the barn at the first damp drop!
The calf starter should be medicated to prevent coccicia. If it isn't then you have to use something like Corid as directed. They will need blackleg and pinkeye vaccination, too. Blackleg is a clostridium (same family as tetanus, botulism, anthrax) and is in the environment. Young stock under two years old at highest risk. You don't usually see any symptoms, just find them dead. When you touch them, especially about the legs, they feel like a sponge full of water, crackle and pop, as air is between skin and muscle. You will never forget how that feels, nor mistake it for anything else once you have one die this way.
Jersey crosses are great, tough little boogers that grow off well. Lots of good experience on here.