So should I try Tam's Foe at level 30 or wait till level 35 to avoid the horrible luck I have with Flowing Hellfire?
I think I did it at 29 (maybe 28). Tam's Foe never did any consecutive Flowing Hellfires, just every three or four attacks. Meiling, Remi, and Yuugi were all able to take the hit while wearing a Bomb Ring (they also had some +FIR added through skill points), for the last slot either get another character that can take the hit or a sacrifice that would be mostly useless for the fight. My Minoriko was capable of fully healing everyone, Reimu would patch up the characters before (and sometimes after) a Flowing Hellfire as needed and buff them before it.
Just swapping out the squishies before the next Flowing Hellfire was enough to keep the casualties down to a minimum. Immediately after a Flowing Hellfire I would usually switch in Minoriko since Remilia took the most damage from it (always had < 300 HP afterwards).
Having Aya and Sakuya buff your other character's speed is a good idea. You don't need Aya out constantly but it helps immensely with your party's damage output (
especially on Patchy), Aki's healing and buffing (it's low delay anyway), and letting your tanks attack/recover SP faster.
Wriggle is still useful for the fight. Switch her in to apply Comet on Earth then get her out of there unless you want to use Butterfly Storm (I had other characters with SP that could do more damage). Irremoveable Shackles is useful for the PAR, but I stuck with Supernatural Phenomenon most of the time because the damage is much better and the former's PSN is weaker than Wriggle's.