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.