Well I got tempted because Jack is by far the best assassin for a long time and also provides a nice bonus for the socks, but ofc I didn't get her... ended up rolling three times and didn't get the 5* CE either

Guess my luck has run out, I only get 5* when I don't aim for them (besides Waver, but that was in the guaranteed gacha). Oh well, at least I got three copies of the 4* CE and two Nursery Rhymes, though one would've been plenty xD With that I again own all Casters available in the game, for some reason I seem to attract them hard, like the totally unexpected Tamamo I got during my second 10 roll back then wih Halloween
good news for Merlin? Better not even think about it
Oh well, this event still seems like a lot more fun than GudaGuda, with the whole raffle thing. Had to push some Servants, because even the 20AP node takes annoyingly long with the bonus Servants I own (Marie, Martha, Nursery Rhyme) + using Robin (who's prolly by far the best 3* to use in this event) and some other 3.
As for grailing, it's MOSTLY done for Servants you love and like. Honestly, you have to use 5 grails to get a 5* Servant from 90-100, and most of the time the difference isn't really that huge. Use it on Servants you love, because strategy-wise it's not of big importance. Personally I grailed my Saber Alter and Herc to 90, but they at least get 5 levels per grail until 90, and I like both quite a bit, so it was a win-win for me. 100 I would only do for Saber Alter, but I haven't decided yet.
And IIRC, FGO JPdidn't even have 40 Grails yet, so it really is a damn rare material. Still, that allows you to push seven to eight 5* Servants from 90 to 100, so there's no need to be all that worried if you don't have like 10 favs you wanna get to hundred, though ofc it will still take around one and half years until we get anywhere near that Grail number on the US version.
TLDR level servants you love, let your heart speak, not your brain. Though naturally, a great Servant can become slightly greater with a Grail, so if you love none, just go for the ones you think will stay most relevant or are all-around awesome.