Free quests first or suprise/party quests first?

Its my first time playing this halloween event. I currently have 1 maid in halloween, 2 halloween princess, 3 trick or treat and a jack o lantern. All of my event CEs are from the shop except for 1 trick or treat. To clear the shop, what is more efficient? To grind final stage free quest till I have all the shop CEs or to do the one time quests for guaranteed pumpkin and get the shop CEs faster?

Also, side question, the guide says never to farm for petit cakes, does that mean not to bother getting all copies of trick or treat in the shop? Thanks in advance.