Yeah, doesn't hurt to start saving now. You'll need something like 5,000 Mana Prism by the time New Year's comes around, to fully LB Da Vinci's CE. Fully LB'd, it gives you a pretty substantial bonus to your QP gain and is one of the better utility CE. The one following it, Chaldea Lunch Time, is another recommended one, as it increases the rate of gain for Bond points which, as you know, takes a long tie to earn normally. So that CE is also well-regarded in-game.
So yes, you want A LOT of Mana Prisms. Later events will reward you with a decent amount, but you'll probably want to do some grinding on the side, especially if you want to max LB both of the aforementioned CE. Just do the 30AP ember dailies and burn the silver cards.