I'm wondering what are the mechanics involved in being able to handle higher difficulty levels once you have a character at level 70. I tend to do bounties and rifts and I up my paragon levels and slowly I seem to be able to cope better at my current torment level so I go to the next one, but I don't really understand specifically what it is I'm doing that is making the current level easier.
Obviously the buffs provided by paragon points help to an extent, as does the cube powers, and finding and equipping better gear. I suppose mostly I'm wondering about the better gear drops. Is the quality of gear that drops related to the Torment level I'm playing at? Is it, along with probability/randomness, going to be some function of the level of my current equipped gear, or my paragon level?
With regard to set items, gear that I have at Torment I is not going to suffice if I try to step up to Torment IV. Should I be looking to craft a new version of a set item to replace it? And if so, what aspects of the game will determine that the newly crafted version will be better than my current version? Is it purely random?
tl;dr: how do I give myself a better chance of ensuring my gear levels with me in the end-game?