I think you’ll find that rearing pure dairy calves is a specialist job and you’re unlikely to be able to make it pay. See if you can find the sort of thing you’d be selling, at the age you’d be selling it, getting sold, and see what they fetch.
If you’ve a market for rose veal meat, you might find that works better - take them all the way to slaughter and butchering. If you have some land you can use, that is.
You would, as twizzel says, do much better with beef cross calves. But again, there’s not much money to be made in the first few months; the people that make it pay have land and take them up to 14 months, or finish them. And even at 14 months, folk won’t pay good money if they don’t know the producer, and so be sure they’re getting a well-reared animal that will finish well.
If you do decide to give it a go, my advice would be to buy nothing younger than one month old, at least until you’ve done it a few times and know what you’re doing. (If they’re going to die, they usually do it in the first few weeks

). The extra cost of slightly older calves will more than pay for the loss of a younger one.
Basically the process is :
Milk powder as per the bag, usually three times a day up to one month old then twice a day until the bag is finished. (One sack per calf, usually takes them to around three months.)
Bed on clean straw, give them some fresh every day. (On top of the old.). They’ll play with it, eat some, and lie on it. It’s essential they eat stemmy forage from very early on to get the rumen to develop properly. My ex-BH (very experienced cattle farmer, and had been rearing calves on a bucket for fifty years, as well as breeding his own) used to give them a little lovely fresh soft hay every day too.
Calf crunch or a starter calf feed should be offered from about six weeks. Again, they’ll play with it at first but will get used to it and start to love it. You want them to be eating it well before you wean them.
They’ll lick at each other’s navels after feeding and can cause real damage. Best to clean their faces up when they’ve finished their milk, and distract them until they forget they were drinking milk. So giving them their fresh straw after their milk is a good tactic. And once they’re eating pellets, you can give them a little of that after milk to distract them - but not much at that time, just enough to take their minds off milk.
Once past the first month, pneumonia and bloat are the two biggest risks. Pneumonia is a factor of housing and cleanliness, bloat is all about feeding. There’s lots of info on here about developing rumens and overfilling milk stomachs, also introducing young ruminants to grass. (Look in Sheep too.)
Hurdles will be fine for the first month or two. After that you really need good quality purpose made pens. Again, the calf you will lose when it breaks its leg will pay for quite a bit of good penning.
I’d agree that buying from the mart can be risky, especially as you are a novice. One tactic would be to go there and watch the trade a few times, see who is selling calves you like, and ask them if they’d be prepared to sell direct to you.
Oh, and get polled or dehorned castrated boys. You don’t want hormonal girls trying to escape

.