Diablo Game Questions Can anyone give a quick rundown on how to go from the free class set to doing endgame runs?

So I've played D3 off and on since it came out, mostly off, and I'm trying to actually get to endgame for the first time this season. In Season 5, my spike of playtime really, I managed to get all the way up to the Champion level of the Journey by bashing my head into objectives until I succeeded via luck. I didn't really have any clue what I was doing once I dinged 70 though short of just repeatedly dying to high torment enemies because a checkbox told me to.

In this season I have my set from the Journey, and I'm kind of lost as to how to actually proceed. I know that you do regular Rifts on low torments to farm legendaries, gamble away a million blood shards for more, and do the act bounties for materials. What I don't really know is what I should be prioritizing to get my character up higher efficiently.

Most of the season journey things right now (Slayer) are clearing things on T7, but I don't feel like I'm anywhere near capable of accomplishing that right now. It was a struggle to clear a T5 Rift. Should be upgrading weapons from rares, or grinding rifts hoping for better set pieces to drop, or doing bounties and rerolling what I have or...? Right now I'm doing a skew of bounties and T2 Rifts, but I feel like I'm not really making even a tiny amount of progress after something like 6 hours of playtime after finishing the starter set.