Brennski got it right about what SCH does in endgame currently, couldn't have said it better.
Of course SCH can do so much more on easier content, but I guess the same applies to a lot of jobs.
If you have to gear your SCH I'm not sure what your priorities should be. It kinda depends on who's gonna help and which other jobs you have available to go with your friends farming gear for your SCH.
1) Weapons: You need to get a good ilevel weapon asap. Akademos is the best for SCH, not sure you should even bother to use SCH before you get Akademos but if you want I guess uh... eminent staff from sparks? Better than nothing. Or the newly added Argosy staff if you have 50 Job Points already on SCH (required to equip it)
2) Gear: AF/Relic/Empy armor
There used to be many useful pieces within these 3 sets, but not anymore. Can still find a use for many of them as "entry pieces" but honestly if you're a returning player it's gonna be so much effort to farm all the necessary stuff, that such effort is better spent trying to farm even better armor pieces (Merlinic!)
A couple of these AF/Relic/Empy pieces are still useful but for very niche use (Boosting Sublimation, Regen Potency, Boosting Stormsurge, etc). Out of them the most useful one is probably Pedagogy Pants+1, boosting Tabula Rasa duration by ~30 seconds.
3) If you can manage to get them fast until the end of the month by farming Ambuscade, try to get as many Jhakri pieces as you can, or even Jhakri+1. None of them are "Best in Slot" pieces, but some are really nice and can be a really fast-to-obtain entry set for your nukes, idle refresh and various other purposes until you get better gear (Merlinic!)
4) Another armor set you can farm is the
Amalric Attire set. You need a cursed item (which you can make a friend craft or buy for gil on AH) and an Abjuration (that drops from NMs in Escha Ru'aun). Hands are mandatory for your nukes, so you might as well get them now, even if they're just NQ. The other pieces are nice but if you can obtain Jhakri+1 honestly I wouldn't bother too much about NQ Amalric.
Don't forget Amalric set can be augmented (fixed augments), can see the 4 different possible augments of each Amalric item in
This page
5) You're also gonna need Jewelry. A safe thing you can buy from AH is Mujin Band, kinda mandatory for nukes. Then Acumen Ring is a cheap (comes from spark) and decent entry-level nuking ring. There's another very cool earring (Barkarole) that can be obtained from a quest and another (Friomisi) which you can buy on AH. As for capes the best is the one that comes from Ambuscade, can get it at the same time as you farm your Jhakri pieces :) If you really want something to use before that you can go for a cheap Toro Cape or a Seshaw cape if you need further Magic Burst bonus to reach the cap of 40%. (yes, one of your priorities should be that of getting as close as possible to the 40% cap for your nuke midcast). Last jewelries you'll need are Neck (need to farm one from the Tenzen High Tier Battlefield BC, meanwhile you can use Sanctity Necklace droping from Quentzacoatl, Domain Invasion wyrm battle in Reisenjima zone). Last but not least belt. I don't know what to suggest here, other than Obis for nukes (you will have to farm all 8 obis and then "merge" them into the new obi through Synergy, can have a friend do that) and Acuity Belt+1? Easy drop from Unity NMs, and one of the best belts for Helix I think.
I forgot about ammo. The best is Pamphredo Tathlum from Reisenjima, until then there's a few nice ammos you can buy on AH or even one you can get from Unity (Ghastly Tathlum +1 if I remember the name?)
Oh and I also forgot about the grip. Ungh, there's many here, I'm sure you can pick the ones you like most. A decent one comes from the Leviathan BC which gets spammed quite often so that would be a fast and easy to obtain grip.
6) You'll probably need other sets as well. A set focusing on Fast cast to use as you precast gear. Then a cure potency set reaching 50% CP bonus for your healing spells midcast. Then probably another set focusing on Magic Accuracy for your enfeebling sets. Jhakri set is already a pretty good starting point for magic accuracy honestly. From there you can go unto Chironic and whatever else you find having more macc/stats.
7) There's also the Enhancing Magic duration set, like discussed in the other thread and here.
I think this is incredibly useful, but then again I'm not sure I would go for that before I have other more basic sets, but that's up to you of course!
I surely forgot many other useful items/sets but I think this gives you a pretty comprehensive guide on what you can expect to be doing for the next weeks! Numbers are kinda random, not priority order.