1. It's not worth worrying about 380 gear at this point, because you're not doing any content that requires it! Your i255 gear will be fine for everything up to the start of Stormblood, and dungeons synch you down to a lower level anyway.

Buying Lv66/68 gear will be plenty to get you through all of Stormblood content, or It's likely that cheap Lv70-72 gear will be on sale once Shadowbringers releases, since a lot of people will already have stronger gear from Stormblood endgame.

You can also look at picking up a second class to share EXP so you don't get quite so overleveled. Otherwise you'll hit the limit and miss out on a lot of EXP from quests.



2. Other people have answered your question, but I just wanted to point out that they're not "tombstones" but tomestones, ie. "book-stones".

Functionally they seem to be like USB sticks.



4. The Lv50 Crystal Tower 24-man alliance raid is going to be important for the upcoming expansion story.

The Lv50 Binding Coil raid finishes off some aspects of ARR and has some character development for Alphinaud and Alisaie. They are particularly difficult gameplay-wise, and most people will play them unsynched to clear them. (Also, there are some long in-dungeon cutscenes like the Lv50 final dungeons, so it's a good idea to play with a party who won't mind waiting for you to watch them.)