Cartridge and cal choice really depend on the impact energy you want at distance.
If you are hunting, then bigger is better ( to a point).
If you just want to shoot rocks, or paper, then LR starts with the fast twist 223 and goes up from there. Although not ideal, a fast twist 223 is 1 mile capable.
Accuracy requirements and budget also come into play. So will recoil.
If you are competing in F class, that is one set of requirements. LR BR, another. Just trying to smack a milk jug, you may find todays factory rifles more then adequate if they get properly bedded and good ammo loade
So let's hear more about your goals. Don't worry about the gear cause that is easy to sort out ONCE you know what you want to achieve and how much you want to spend.
If you visit my website, I have a series of articles that can help you get started and covers the rifle build, reloading and optics. Also, has some of my recent project rifles so you can see what is possible.
There is no one 'right' answer. Just a huge range of options that you can choose from as you desire.
Fun, fun, fun...
Jerry