It's a long program to buy cows and raise calves to finish out for beef. Then you've got to either have a bull or AI breed the cows.
@Warren Allison is right it might be better to start out with a couple steers.
If you are real concerned about disposition of the animals then my preference is to buy around 500 pound calves be it steers or heifers.
Those calves may not be too set in their ways yet and are young enough to tame down that way you kind of let them grow up around you. That's a common size to buy because it's fairly average weaning size range.
As far as breeds go there's calm and flighty in all breeds so just have to be careful and not get anything that seems real wild or aggressive.
I'd recommend Angus or Hereford, generally should be easy to find decent disposition ones. I'm also more confident in those breeds as far as calving and doing things right in that respect. There can be complications with any of them though.