Yes.

By the way: although I’m currently running through Diablo IV S01, I could run you through some (higher) greater rifts to help father and/or level your legendary germs and get you geared up. Feel free to add me: Dekudibusei#2108. That goes for anyone who needs a hand in here (although I haven’t played seasonal for a while, so I can only land a hand in non-seasonal…).

Just for future reference / completeness: it was temporary, but game-wide and not only in Helltide. They have been re-enabled.

Yes. Once you get to 70 (on your first character; with ‘alts’ (further characters, after you’ve heard your ‘main’), a new option called Adventure Mode opens up. There are several activities for endgame: bounties and nephalem rifts (always available, and always at the difficulty level you’ve set when opening that ‘instance’ (the game you’re in an that moment), and greater rifts (which have their own mechanic for pushing higher and higher, along with their own unique reward system (blood shards that can be gambled at Kadala, and powerful legendary gems with their own affixes).

There are a lot of resources available online to guide you towards and during endgame. You might want to riffle through the YouTube channels of, say, Rhykker, Raxxanterax, Rob2826, or one of their colleagues. I personally like Raxx’s content a lot.

EDIT: 100 points extra for your username, LOL. Even in-game, hahaha!