1. Yeah, ill re-up that you should be able to safely ignore the i380 level. While you could get there with some help, it wont be necessary. The gear you have is good for another 5-6 levels of story. And by the time youve gotten that far...

2. So you arent quite there yet, but the story is going to send you to the "end-game hub" for the HW expansion fairly soon. In Idyllshire you should be able to find an NPC(you might have to finish the main HW story first) who sells gear for Poetics at ilvl 260 which is upgradable to 270(also for Poetics - this gear level starts to show its limits around level 65). Once ShB drops, the NPC in the hub area for SB should have the level 70 versions for Poetics too. So youll be able to get some upgrades with your tomes. And in the meantime, turn some of them into cash. Demicrystals or gardening soil(grade 3 thanalan) are good bets.

3. Any at 100% spiritbond you should for sure convert to materia(to use or sell). Any colors just turn them into seals, and the whites become pocket change. If youre full on serpent seals then spend some. Get a few hundred ventures, find some crafting mats to sell, pick up the chocobo bardings. No point being capped on a currency.

4. As others have said, the level 50 raids bear some meaning on the overall main story. The 8 man raid closes some of the calamity storyline very nicely. The alliance(24 man) raid appears to be linked in the story to the upcoming expansion(details have yet to become fully clear). The other raids, so far, are mostly filling in side-story and lore rather then being tied to the mainline. The 8 man raids for both expansions resolve the stories for powerful beings in the FF universe(Alexander and Omega). The alliance raid for HW adds details to the war of the mages and some other FF14 backstory. The alliance raid for SB is a bit about the history of a region, a bit about how the garleans see themselves in the world, and a lot of fan service for those who played the Ivalice games(FF 12 and Tactics mostly).