Speaking of, if you want a relatively non-spoiler overview of the event, with tips, Kscopedia has you covered here. I admit, I'm still fine-tuning my supports. For instance, when the Caster node dropped, I switched the CE on my Santa Alter, because oh, now it makes sense.
The event is understandably tough, given the prerequisite. Thankfully, since the nodes are single-type, you could build single-type parties and dominate them, but doing so means you miss out on bonus drops, so some diversification is recommended. Thankfully also, bonus drops are sprinkled among rare and common Servants alike, so you're probable to have something that gets you bonuses, even if that something is Mash and the Christmas Welfare Squad (now featuring Altera).
Honestly, the thing this event is doing is making me like Altera, which I didn't expect. I mean, sure, she's been a chuckleworthy deadpan at times, but I've never considered her cute until now. Apparently, this version is closer to the green facet of Titan Altera - that is, more "cute" and "girly" than "fierce warrior" - whereas the Saber version is closer to the red facet. I gotta say, the sneezes are inexplicably adorable to me.
The sheep help too.