Really depends on how you want to play it. You could go for (what's considered) optimal BiS gear only, you could go for "wasted" mythology spending like on your gloves to make up for an accuracy need, or just go with what upgrades you can. Personally, while I'd love to just buy what I consider BiS and save my tomes for another class, my Allagan luck has been non-existent over about 35 chest drops, so I've bought gear I probably won't end up using within a month or two. Anyway, what BLMs should probably go for (no real math to back this up, sorry):

Relic+1 > (accuracy increase on gloves, feet, chest, or belt if it can't be made up with Vanya pieces or food) > Myth Ring > Myth Necklace (Allagan Necklace is T5) > Myth Bracelet > Sorcerer's Petasos (considered BiS hat, if you can afford accuracy loss) > fill in the rest based on what you haven't gotten yet.