I am a UU myself, and have downloaded some religious custom content, but for the most part, my Sims just go about their daily life much like I do - The Sims 4 doesn't have a ceremony to attend on Sundays, though I suppose I could add it as a holiday or event for every week. Instead, I prefer my Sims to reflect their faith in their actions, and do not worry myself about what the pixel people believe. Some of them might use one type of religious decoration, others might have a different type of religious decoration. I have added a "Bunny Day", complete with Flower bunny, religious ceremony and egg hunt, and a "Spooky Day" to calendars in some of my saves. Storytelling features prominently on my Spooky Day - it wouldn't be the same without spooky stories. What I don't do is create rival religious clubs and set them against each other. I dislike that level of drama in my game. Sometimes I even move Love Day so it comes before Bunny Day, and I usually add "watch romantic tv" to Love Day.
In one or two of my saves, I also added a Summer Solstice to the calendar since summer had no holidays in it, and in another one, I added an Independence Day, and a "The Big Game" Day. It is too bad they didn't add "Light incense" or "Take mud bath" to the list of holiday traditions that are selectable (it would have been perfect for an "At Home Spa" Day, among other things). "Read book" could have also been a tradition.
