We wean at 6 to 8 weeks of age, you want to get them upto eating at least 1kg of concentrate before you wean, we use a a 18% ration that we put in front of them after the first couple of days and they will soon start nibbling it and from day one they have water in front of them at all times, bed them down and feed them barley straw not hay, the straw gets the rumen activated and working. We only feed warm twice a day at approx 39.c invest in a bucket thermometer and be exact with your milk powder measurements, not that "will roughly do" and make sure you a meticulously clean with all milk buckets, whisks etc, feed intake depends on what age you can get them at the older the better for you!!
Ours start off in pens then once they are up and running get put into batches of 10, as a guide they are on 6, 8 an 10 litres a day for weeks 1, 2 and 3, this increases then decrease as you wean, shop around for your milk replacer but use a good quality one. I wouldn't pay a huge amount of money for the jersey bull calves as they would have probably just been shot anyway, jerseys do have a reputation but I've only seen it in much older animals, personally I wouldn't use rubber rings, you could keep them entire as you will be killing them early, some say they finish better entire, we use burdizzo bloodless castrators, cheaper than the vet and less messy and less risk of infection. watch out for pneumonia when they are in, keep drafts off them but plenty of air above them so all the crappy air is blown away. If you buy them now they'll be an ideal age for turning out come spring. dont try and aim to fatten em right up, fattening a jersey is like trying to fatten a greyhound you never will.
You wont make a huge amount of money but as long as you do the job right you'll have loads of fun, will become addicted to having cattle and be eating your own beef.. Hope it all goes well for you....