How hard are the Halloween / Christmass RERUN events?

Here's the SQ math: https://www.reddit.com/r/grandorder/comments/77wnxc/heres_an_estimate_for_how_much_quartz_and_tickets/

Halloween Rerun:

Just completing the story will grant you Caster Liz. You could run the easiest nodes on the story and still get her. The only thing you might have trouble doing is grinding enough event currency to get her to NP5. You have to use different shop mats to buy 4 Lizzies and that takes a nice chunk of time dedicated to farming nodes if you have a lower leveled roster. Higher level servants -> Harder nodes you can complete -> More mats you can get. If you're satisfied just owning Caster Liz, you can save apples for the Saber Liz event that runs right after it.

Christmas Rerun:

This one isn't as grindy, but that all depends on RNG. This event follows a lottery system and you have to farm event mats to roll the lottery (that means you can farm a node once and get altria in a roll, or have to farm a node A LOT of times just to roll altria). Farm mats -> Roll the lottery -> get a Santa Alter ticket -> refresh lottery -> rinse and repeat until NP5. This is time dependent since re-reuns are indefinitely shorter although only by a few days meaning farming the hardest nodes here is important. By the time Dec rolls around, you should have servants in the 80s so farming shouldn't be an issue for you.

Not very hard at all. After all, those were some of the earliest events in the game, so they were designed mostly for low-middle level players and they are not going to be changed for the rerun.
I remember making it through Halloween just fine with only 40-50 lvl servants and only one gacha CE. Honestly, a good support can probably solo any of the free missions. You'll might have to drop some Command Seals for the challenge missions though.
Christmas is a bit trickier, you'll probably have to do easier missions first until Santa Alter unlocks a few days in. After that you level her ASAP and farm the 40 AP mission - your Santa + support Santa should be more than enough for that. Don't bother with the 50 AP mission unless you've got a full bonus team that can reliably clear it (it's a bit more efficient but you'll do just fine without it).
Also don't skip Prisma, are you crazy lol

if it's one event you shouldn't skip, it's Prisma.
I think I read somewhere that even jp hasn't done a prisma rerun(need someone to confirm) and they're ahead of us for liek, 2 years?
and Kuro(Chloe) is a really good SR archer

You can definitely clear every event in the rest of this year except nerofest without skipping much even with low team lmao. I started one month earlier and totally cleared fate zero event(21 day event) in literally 3 days with only 1 ssr when my account is one week old, only one servant lv 60 , 1 lv 50, and the rest lower.
All you have to do is read guides, make a good team, and play wisely, even a team of ascension 1-2 servant should be able to clear most event in the rest of this year that is not named nerofest. Unless you only play a very short time every day.

Why would you skip prisma....
Kuro is arguably the best welfare servant in fgo, tied with kintoki rider. With np5 she deals 1500% dmg and can np spam, and have an evade.
Even if you have ssr archer, she is the second best single target archer after summer artoria so the only reason for someone not to raise kuro is if they have archuria lol.