Hey Buukki I can tell you what I think is the highest priority or skippable in the list you made.
Keep in mind, it goes without saying, it's just my personal and highly subjective opinion and not a "fact"
Assiduity Pants +1.
You might not need the perpetuance, depending on your build, but they're nice to have regardless because of the refresh and can be used by multiple jobs. The augmented version can be used in a pet-engaged set, but tipically those are not very effective on SMN, compared to like PUP and BST.
Lamassu Mitts +1
These can be used for avatar engaged sets (but see above), for Perpetuance according to your build, even if just as a temporary placeholder. They used to be pretty nice for SMN skill sets but they're no longer the best. Can be a temp placeholder as you aim for Baayami +1
Wouldn't say these are "vital" but UNM campaign is up, they can be a nice and free placeholder.
Asteria Mitts +1
These can be nice (augmented) for pet macc BP sets, until you get better options.
Primarly I'd say these are a nice idle set because of the refresh+2, unless you have augmented merlinic for that.
Not vital, can be nice.
Body for sure, get +3 asap.
Head can be a nice temporary placeholder for refresh if you think it's gonna take you a long time, for whatever reason, to get Empy+3 head, because otherwise that's the piece to aim for in the head slot.
Can skip the rest (feet offer a nice option for perp but with Apogee-1 and empy out there I'd skip em)
You want head for the enhancement to Astral Flow duration, but you don't "need" +3 for that. You could stop at +1, hell you could stop at the level 90 augmented version.
Body is an interesting option for BPs like Volt Strike, Predator Clows, I think Hysteric Assault too? Basically for multihit BPs with FTP transfer. If it's better or worse than other options is a complicated issue, which has been discussed in depth multiple times in this thread (please notice there's no pet: acc on this body).
I dunno what to suggest here, consider this option for sure but maybe don't prioritize it?
I'd say you can skip the rest of relic armor.
Head is a must, totally. Get it asap.
Then there's hands for Mana Cede, but honestly you could use the +1 version for that (or even the abyssea version). And tbf is not like you use Mana Cede every time CD is up, so...
Body can be a nice temporary option to reach the necessary thresholds of Perpetuance and SMN skill (need to never go below a certain number of SMN skill to mantain the boons of Avatar's Favor, read further in the thread or BGwiki to see the tiers) but that's it.
For feet I can say similar things I said for the hands, with the difference I'd dare to say Elemental Siphon is used more often than Mana Cede.
Legs are very nice for some support BPs (healing) that scale with TP and are very nice if for some BP sets you want to aim to as much Blood Boon as possible. Both uses are very niche if you ask me, so I wouldn't prioritize them.
Empy sets have another secondary nice use, DT for the master, while also giving very nice defensive stats/meva etc. Up to you if you want to get em or not, depending on your available gallimaufry.
Apogee+1, HQ for the set bonus.
You want at least Head, Legs and Feet. "Pro" SMNs probably go for multiple of them, one path A and one path B. I'd say you can just get a single one of them and go path C for all-purpose. You can always change your mind and get a second pair in the future since you can swap the augments.
This is gonna be expensive but you kinda want at least 4/5 Baayami+1: body, hands, legs and feet.
These are used for various purposes, for SMN skill sets (most support BP: ward) and for several other instances where you want to reach a certain amount of SMN skill when precasting BPs, for Avatar's Favour and to reach the desired amount of -10 BP recast, bringing you to the current cap of 20 seconds recast (which is a pretty big difference compared to the raw value of 60 seconds)
You at least want a pair of Merlinic Hands augmented with >8 BP and whatever else you can get. Ideally you will end up with at least 2 of them with different stats but you gotta start from somewhere, right?
Helios can still be nice for multiple stats but first and foremost BP damage paired with Pet: DA. This works very very good for BPs with multiple hits and FTP transfer, like the ones I already mentioned.
But I'd say this is a very pro and dedicated set. You might want to work on those eventually but I'd say probably not right now?
Also I suggest to get Enticer's Pants from Sinister Reign, ideally with the max augment but anything works.
They are very very nice for magical BPs and they're free!
Furthermore, there's other things to discuss:
The best is the Odyssey one, from R20 onward (probably even earlier).
Second best option is the Sancus Sachet +1, which is SU-something.
Next best option is probably Seraphicaller I guess?
Leaving Stage5 Opashoro and R15 Nirvana aside, there's something else you want
Espiritus path B is nice for SMN skill sets (most support BP Ward). If you have multiple ones of them, then Path A or C can also be very nice for magical BPs, until you get better augs on the following ones.
Gridarvor - get it and augment it. It's gonna be your best idle staff for perp (until/if you get Nirvana), it's also an incredibly strong option for phisical multi-hit TP with FTP transfer.
Grioavolr / Keraunos - these can be augmented with BP damage and several other stats, turning them into your best option for magical and even physical or hybrid. Grioavolr is potentially better but augs are more random. Keraunos gives you a minimal degree of control with the 3 different slots/stones. They can be easily better than Espiritus path A/C for magical BPs.