The shared chest should be like Destiny 2's where all of your glams, weapons (In Desinty 2's case, Ghost shells and Sparrows) and such can be shared between all of your characters, that would go a long way of reusing older gear for your alts working their way up the msq. Destiny 2 also has a collection system where it cost a few tomes (Legendary Shards in D2) equivalent to get any gear and weapon you have collected in the game so far anytime you want, even out on the field.
All Mogstation purchases should be accountwide, I really hate having to buy the same glams over and over for my alts, so sometimes I'm forced to pay three times so that three of my characters can have a specific Mogstation glam. SE can't use the excuse of glams not being able to be made accountwide when I have a glam that is accountwide, the Far Eastern Journey set that was an Amazon preorder bonus for Stormblood and all of my characters get it when I create them.