This project is beyond simple "red flags." It can't be made, especially at the goal that's stated.
Vovk, you've stated
here that your printer is "most likely" going to be USPC. A simple 2,500-deck print run with them, plus delivery to your backers, will run closer to $10,000-12,000, and that's a stingy estimate. You're also offering plastic decks and mini decks, all for merely $5,000?
The only way you'll be able to get away with making this deck that cheap would be to use MPC, a manufacturer that isn't making cards in the USA. As far as plastic decks and minis - even if you used USPC, they don't make their own minis; they farm out the work to a Chinese printer. And their plastic decks would blow the lid off that goal of yours, sending it sky-high - plastic decks are EXPENSIVE TO MANUFACTURE.
I've seen exactly one custom plastic deck, and it didn't even use custom faces except for the Ace of Spades and the Jokers - that was the Karnival Death Heads Armour Edition, made in Vitoria, Spain by USPC subsidiary Heraclio Fournier. They sold for $25 a pack, and weren't hot sellers. Subtracting out the two paper decks you offer with it at the lowest tier it's available, you're offering it for $26 with US domestic shipping. Seems a bit lowball to me.
There's so much here that doesn't add up, financially speaking, that i wouldn't touch this project with a forty-foot pole, no matter how gorgeous the cards may look. If it funds, and only by a narrow-enough margin, you're going to either lose a huge amount of money or you're going to shortchange everyone who backs you, be it unintentionally out of inexperience and lack of knowledge or with intent because you're out to rip them off - none of these are pleasant alternatives. Either that, or you lied about using USPC and are using some other printer as yet to be mentioned, in essence creating a bait-and-switch.
No matter how you slice it, this in its present state is a toxic project, doomed to fail even if it "succeeds."
Vovk, if you're serious about getting this made, shut it down now, get a printer and get someone to help you figure out the REAL costs involved in getting your decks made. Make the plastic decks and mini decks STRETCH GOAL ADD-ONS, not part of the initial project goal, because it's hard enough to produce a single deck, never mind three. Then, once you know the REAL costs of making a deck, make a project that's realistic in terms of the minimum cash needed to get it off the ground. Without that ground work, this project is barely more than fiction.
BTW: you misused the word "triduum". Its definition is "three consecutive days of religious celebrations leading to a feast" or at the least "three consecutive holidays." It's most frequent use is in referring to the three days starting with the mass on the evening of Maundy Thursday, continuing through Good Friday and ending with evening prayer on Easter Sunday.
Hallow'een, or All Hallow's Eve, was originally the pagan holiday of Samhain. The Roman Catholic Church moved All Saints' Day to November 1st and started the feast day at Vespers on the night before in order to co-opt the holiday from the pagans. All Souls' Day follows on November 2nd. Originally, there was a feast day for celebrating marytrs on May 13th, with the first record of its celebration recorded on 373 CE, though there are records of a similar day on different dates in different parts of Christiandom. Under Pope Boniface in 609 it was changed to celebrate all martyrs, under Pope Gregory III at some point between 731 and 741, it was moved to November 1st to replace the May 13th feast day and under Pope Gregory IV in 837 it was expanded to include all saints as well as martyrs, becoming All Saints' Day. The celebration period ends at the end of November 2nd on All Souls' Day, lasting just over two days - Halloween to this day is considered a pagan holiday, is not celebrated on Christian calendars and many Christians shun Halloween celebrations.
There's precedent for this with other holidays - the Catholic Church, having no accurate record of the exact date of the birth of Jesus Christ, moved the date to coincide with a Germanic Pagan 12-day holiday period called "Yuletide", replacing the first and last days of Yuletide with the birth of the Christ Child and the arrival of the Three Wise Men.