I want to keep everything pretty typical for the real holidays. For example, Thanksgiving will have a grand meal, family gathered together, and 'giving thanks' if that's an actual tradition available/has a similar variant.
Christmas will have the grand meal, gift giving, father Christmas, and I'm really hoping that since they said we can celebrate/mourn the dead, there will be a tradition that allows us to celebrate birth, so I have have it as close as possible to include celebrating Jesus's birth. Even if there won't be a birth actually happening, I want it to at least be in the list of traditions.
For my made up holidays, it really just depends on what options there are for traditions. I want to create 4 new families when the game comes out to play in each season, and I really want to create a unique holiday for each season. So I guess once we find out all of the traditions I can decide what holidays I'll be making.