I want to level all 4 classes but I do want to know what is worth farming so that I can share with my other characters. Are cash, erydium (purple cash), difficulty level unlocked, accessories, skins, and challenges shared with other characters?
Bank storage and related SDU slots, weapon skins and trinkets are all shared between characters. The rest, however, is character specific.
With the bank being shared though, you can use that to keep things for new characters to use.