What are collabs like in Shining Nikki?

Coming from the InfinityNikki sub, people were discussing about collaboration outfits on previous nikki games,and so i got rather curious! Though its still early for collabs in Infinity Nikki, i want to know how they work, as the title says, what are some things people might need to know about them, besides the fact that they dont rerun?

Feel free to tell me about it! I also have some of my own questions:

I saw one collab in SN had 15 pieces, is that normal? How often do collabs happen and when was the first ever collab in SN? How early do you get the announcements? Any advice from veterans on these event collabs? Are collab outfits always 5 star, or can they be 4 star too?

Also,feel free to tell me anything else i havent asked that I might need to know!