Q1. The idea is to identify future trends not trends already in the mainstream. If your ahead of the game it does require perseverance, faith and patience. You'll generally identify when you've got it wrong due to an alternative trending name replacing your chosen bet. The market is going to make its choice Not you. Don't hold on to domains that have already been superseded.
Q2. Once a name is already trending it's hardly likely that you'll be able to hand-register a Good domain. Don't settle for a minor extension. A Good play on an emerging trend can indeed be profitable but, you'll need to get in at the beginning.
Q3. Absolutely Not. Trends are Niches by nature. Only the very best 'adopted' ones stay/hold the test of time.
+ There is a reasonable argument for selecting a super-trending EXTENSION to go with new-trending domains and I can see the appeal. Just make sure you pair-up in a way the domain market wants to buy.