Tried boss rush at Normal, after 4h boss I always left with 3-6 hearts and both potions used. And 5th boss always finishes me off with L2 wizzrobe spam. 180 - 400 rupees down the drain. Have fun grinding with little to no hopes for success. Or sit through super long save loading downtime.
Checked bosses in editor, all buffed except 5th and 12th ones. Mostly HP buffed and more randomnaku.
I didn't use any rupees during the boss rush, because sword does more damage, for the first boss I used remote bombs on the heads. and I always had roc's feather equipped