Should I do the story or farm dalies

If you haven't already, Edward Teach's Interlude gives you 10 forbidden pages as a reward. But if you have, then Hyde Park in London is your best bet (30%).

I would farm ember quests until the 1/2 ap event ends and then farm the pages afterwards

I know the feeling. I've still got exp cards from Nero Fest, plus we've got this 1/2 AP ember gathering thing going, but every servant that I want to level right now needs Homunculus Babies for ascension. I'm only at the beginning of Septem right now, so London is pretty far away.

But spell pages seem to pop up pretty often in events, either in the shop or as a drop from the actual nodes. If you only need 8 of them, it's probably not worth missing out on these 1/2 AP exp cards over. I bet you'll be able to get them in the upcoming events, and as a worst case scenario, it seems like we should probably be getting 1/2 AP story mode before long.