It didn't take long to get from 60 to 66, but now it's taking forever.. I'm 68 and doing bounties seems to give slight-to-no exp.. I lucked out on good equips, so I'm stuck doing bounties on hard till I can get better equips (at 70)...
Also, at 70, do I just do rifts & bounties?
Do I do easy rifts till my equipments get better?
Well the fastest way would be getting carried by 3 people in torment 6, but i guess that´s not what you wanted to hear. As for single player, every playstyle is more or less viable.
if i were you, i would lvl doing act 1 bounties. The reason behind this is that you can get a decent Royal Grandeur (and you need to farm it at lvl 70 anyways).
Also, at 70, do I just do rifts & bounties?
Do I do easy rifts till my equipments get better?
& No, I don't get a key after every bounties..
Your first bounty from every act will not grant you a key (to avoid abuse of doing an easy fast bounty to farm keys).