You Spoony Guide! - A Troubadour's Libretto

Head => Etudes. Gives a +1 stat and +20% duration compared to the "regular" options if you get the HQ, just +10% duration if you get the NQ. Imo NQ is useless, HQ is ok but pretty expensive for what it offers. Etudes are very rarely used.

Body => This used to be priority #1 but the game meta changed, threnodies are not as vital as they were during the era of SC+MB strategies, so it's kinda up to you. They give a potency boost to Threnodies in exchange for magic accuracy compared to regular options. NQ can be worth too but, if you ask me, I don't see Threnodies as vital as they used to be in the large majority of fights.

Hands => This will probably be the piece you should get above all. NQ at least, HQ even better. It boosts the Carols songs. Which are rarely used, true, but when they are it's really nice to have that potency boost.

Legs => NQ gives a +10% potency to Minne, at the cost of a small duration loss. HQ is 20% potency and a small duration boost. Minnes are very rarely used and when they are it's tipically an "icing on the cake" sort of situation, rather than Minne itself being vital. Kinda up to you. If you ask me NQ not worth it. HQ kinda is, but it's very expensive for what it offers. Up to you and your finances.

Feet => lolmambo. Same thing said for Minne applies here in terms of potency/duration boosts and losses. Ask yourself when is the last time you've seen Mambo used or requested. Imho not worth it.

Song precast set => used to reach (or get as close possible to) 80% song casting reduction time through a combination of "Fast Cast" and "Song Casting time -" gear. If you want you can go even above the 80% cap, to compensate for possible debuffs like Addle.

FC set => this is not "required", it's used to precast all other spells (cures, -na, utsusemi, whatever etc). Multiple pieces will be shared with the previous set probably. Not sure if you can reach 80% FC on BRD with just FC gear. If you can and you will then you could use this set for everything and forget about the previous.

Song Midcast (debuff) => A generic set that will be used to midcast your offensive songs. In addition to a basic/generic set you're gonna need specific variations for songs where you have specific pieces (for instance the Threnody body mentioned above). Stats focus for this set might change according to your goals, but in general it will be mostly Macc. Full AF3 set serves you very well from that point of view.

Song Midcast (buff) => A generic set that will be used to midcast your beneficial songs. This will focus mostly on "song duration +", where that's not available you're gonna use the Empyrean set to benefit from the Set bonus. In addition to this "generic" set you're gonna need a plethora of variations for specific songs, for slots where you have gear boosting a specific category of songs. Same approach as for the debuff set really, but with a lot more specific pieces/sets here. It goes without saying but of course the neck slot will be fixed to the Brioso Whistle +1 for both this and the previous set. Ranged slot will change according to what you're doing but in general it will be Gjallarhorn.

Idle set => realistically you could and should have multiple idle sets. You might want to create specific sets focusing on different stats. One on regen, one on DT, one on Refresh, one on Meva, w/e. Or you can go with a generic set that has a bit of everything, up to you, but you'll need at least 1 idle set for sure.