You mostly can't buy pure beef calves as they are, pretty much by definition, reared on their mothers.
So you will be buying calves out of dairy cows, which the farmer needs off the cow so he can milk her.
Rearing pure dairy calves is a specialist job, so don't go there.
So you will be buying and rearing beef x dairy calves.
The problem with heifers is that they come a-bulling and can give you a management problem. However if you are selling at under 12 months, and any bull calves you have are castrated, then you shouldn't have too many problems. (And you definitely want the bull calves castrated, whether you have heifers as well or not.)
Any of the native beef breeds that you are likely to get are fairly docile - Angus, Hereford, Beef Shorthorn, Red Devon, South Devon to name a few - as are British Blue. Continentals are, on the whole, more challenging - perhaps best to start with something easier.
Depending on where you are, you may be able to outwinter. They will need good shelter. If you are going to outwinter then you definitely want a hardy native breed.
You should go to your local mart
now and see what is being sold at 11-12 months old now. That will show you what sort of size and price your calves would be.
I've said it before but I am going to repeat it - try to buy calves direct from a local dairy farmer, especially as you start out. S/he will give you a little bit of support, you won't have the complication of diseases picked up through the mart, and I won't have to write pages of information about what to look for and what to avoid when buying through the mart! (Which would be hard work when I would have to explain every term, less hard to do when you have a bit of experience under your belt.
)