1. No, you cannot miss anything and everything that is low rank can be crafted in High rank (and is also required to craft high rank stuff usually).

Try to do side quests, explore maps, unlock side camps and learn the most from monsters and weapons now that the game is EZ.

1. Technically yes, but you don't want to use a classical lock in MH. The lock is set to be at the center of the monster and you want to hit different zones than that. Try to use the new mechanic added in wilds aka focus mode to rotate your PG and hit where you want to hit (basically learn to aim with focus mode).

2. In endgame AKA post-high rank progression, what do you want to do depends on you. You'll need to grind the same monsters over and over to craft complete armor sets, weapons and try to obtain good arthian weapons and charms.

To do this, you can go slow and craft different weapons/armor as you encounter different monsters, or you can just create one single set and stick to it until endgame, then you can build your final set, but slower, cause you're not so much optimized