1) Looking for a specific bounty, usually. But it depends on the strategy, so which guides specifically are you referring to? There's many different strategies.
2) You can upgrade gear before or after reset, doesn't make a huge difference.
3) That kind of "snapshotting" is one strategy, yes. I see a lot of people planning to do that. I have some concerns:
i) If lots of people do this, the servers will go nuts and you will wait a minute or so before being able to create a new game. It simply doesn't work if too many people do this kind of quick game recreation strategy. Always have a backup strategy that does not require a new game.
ii) This requires lots of coordination, planning, and practice. If you don't know exactly what you're doing, it won't be any more efficient than just doing what you usually do (kill streaks or rifts). This is an advanced strategy for min/maxers.
iii) The person who does the snapshotting will have a lower level, and hit level 70 quite a bit later. This imbalance is difficult to handle. In general, many people focus way too much on the 1-70 race, when it's actually a 1-Chapter IV race. /u/behindtimes on Reddit made a very nice post about this.
Have to agree with Bagstone on this. I know a couple recent videos have come out the past couple days on Cursed Chests.
First, what you see isn't a new tactic. It's been known for years, though done somewhat differently. I first found out about it in 2017, and I'll admit, it does work, but...
Yes, there is a but. As sVr mentioned in their video, this isn't some miracle strategy that's going to get you to 70 in under an hour. And, as Bagstone stated, this requires a fair amount of practice to pull off. Every season, a few people ask me about this strategy, and almost every season, most of them give up. Why? Because look at the players who have put up videos of this. They're not average players.
For most people, it might get you to 2 hours, if not worse. It seems such a simple strategy, but it's not. Let's say you search 100 chests on your way from 1 to 70, and take 15 seconds apiece. Another player has the exact same games as you, but only takes 5 seconds apiece. That's a 17 minute difference. And most people aren't even taking 15 seconds, they're taking much longer.
I've run a variant of what you've been seeing for awhile now. On a few occasions, I've tried to explain this the day of season, and it never works. Sometimes, yes, it ends up longer than just rifting if you don't know what you're doing.