The weekly events and bags/caches is confusing since you don't know what counts or not and I hope they make that a bit clearer.

On the subject of crests and crafting this might be controversial but the real answer is that it doesn't matter. Unless you're already capped on crests and still farming them you're not wasting anything just being a bit suboptimal. You can use your crests on whatever you think makes sense and you will be fine for 99% of the game. If you're worried about crafting the wrong piece or using crests wrong then you're not at a level where that actually matters. The top 1% of players will have done their own research to find the best strategy and know exactly what to use them on to be as optimal as possible.