Ewer on BLM can be helpful. No, it doesn't mess with our rotation, the only negative is the BLM can get greedy with more than he can handle timer wise, but it's not always a help either, depending on when you used it. I would rather it get used on BRD or a very DPS heavy healer, or, most preferably, Royal Road it.

Arrow belongs to BLM. DRG/BRD/MCH love it too but not quite so much. NIN can't make as great a use out of it as it messes with DoT timers pretty constantly. MNK doesn't like it on average due to TP concerns. SMN is bottom priority, you can only do so many Ruin 3s in Dreadwyrm Trance with or without an Arrow regardless, and getting more Ruins isn't exactly a thrilling use of Arrow.

Balance typically goes to the top DPS in your comp, and fight specifically. If you have a BRD and caster, typically caster will be one of if not the top DPS in the group. If you have a MCH and otherwise your top DPS is a NIN or DRG, go for the NIN/DRG. If you have an AoE heavy situation, the AoE heavier classes will get more, like a SMN. If you have people who are more geared than others, or are particularly skilled compared to the others, go for that person; trust me a strong BRD/MCH without a DRG will destroy the average PUG BLM/MNK.

Spire's typically not needed but MNK gets the most use out of it by far. Royal Road or Redraw it more often than not.