for satori, I just went with level 10~ party, I believe. it consisted of Reimu, Sanae, Sakuya, Mokou and Byakuren with patchouli as commander.
satori's rather easy for a boss, I didn't apply any sort of strategy to beat her. if you feel like you aren't high enough, just try to get a level or two in her dungeon and fight her again. it worked for me with kaguya and eirin. make sure your characters have a set role, though. like using sanae for healing/buffing purposes only. don't do mixes, that will only drain bombs and MP where it shouldn't.
also, I'm on stage 13 now. I guessed momiji would be the boss of stage 11, after all. but I didn't expect cirno. the freeze/attack combo was unfair if you don't expect it to come. but I suppose later bosses will always have some sort of shenanigan. the fgith was fairly easy, though. buffing my resistance with sanae wasn't a sure-way to prevent freeze, but I can't remember any character making me immune to it, anyway. maybe byakuren had something, but I don't think so. eh, that's over with, anyway.
stage 12 was tough, actually easy layout and everything, but after a while, my MP just went down and I was in the middle of nowhere - turning back would let me face all the enemies I left out, continuing would let me face all that's in front of me. I just tried to avoid all in front of me and hoped for the best. somehow worked out.
Kanako and Suwako were fairly easy. once I figured out kanako can be instant death'd, at least. figured it out through youmu, whose sword has instant death effect. Suwako seemed immune to it, so I had to fight her properly. she did have pretty damn high magic resistance, so patchouli didn't help here at all. Sakuya and youmu worked wonders, though, since suwako is weak to all (?) kind of physical assaults. things like slash of eternity did over 2500 damage, with criticals over 4000. that was easy.
now, I think I'll have to fight iku and tenshi either together, or iku first then tenshi. I dunno what to expect from iku (i.e sheer power or some trick that has to be avoided by some strategy akin to cirno/momiji fight), but I think tenshi is going to come at me with sheer strength. I am assuming I need alice for that fight. just a hunch :V expect more to come in the next 2-3 days for that matter