You should definitely try to get all the month's rewards before you get the fafnirs, though. And I'd also get the slime facility first too.
Also, regarding the path through the bosses, there are also weapons for fighting manticore now (they'll damage his OD bar). But I heard those weapons may not actually be useful enough to matter.
...anyway, I ended up being up way, way too late so I ran some of them last night. My thoughts are: kinda not great that both the fights are so easy, and the ghost is 1k might less than them so they'll be the same. They really should try to add Zephyr-tier fights for stronger players along the weaker ones meant for players who are earlier on. And there is an appealing new weapon... but it's the new wind staff for Lowen, which doesn't involve the new bosses. So I guess Vixel's staff is fine at 0UB, and I need to fight Zephyr for a while to make Lowen's instead.
Other thing I noticed is that obsidian golem doesn't even always drop their slabs. But in return, I got 6 leaves 2 out of the 3 times I did it. So that might be the best thing to farm for the month's shop so far, especially if you're using the shop's honey/ashes and want to make sure you come out ahead on leaves.
also I guess I do want to pull, like, once or twice on this banner due to it being everything, so I should maybe buy something for dailies...? hmm, gotta check dia rates on these packs...