Here’s what I do: I let them take over the entire save, then give them their own. XD I’ve had my Yu-Gi-Oh save since July 2019 if I remember correctly. It’s the only save I’ve played for more than a few minutes since then, and I think “all out” would be a pretty good description.
I started with just one household in my first save (I still have the tray files sitting around somewhere). Soon, I added another one, paired everyone else up and ended up with four. In my current save, I decided to make the other important characters too, whether I particularly liked them or not, then added some less important characters, and now I’m seriously considering Simmifying some minor recurring characters and one-shot villains from early in the series, even if they have exactly two spoonfuls of canon characterisation between them for me to work with and I have to invent everything else myself. (What have I done? XD)
If we had more room in San Myshuno, or the more modern neighbourhood in Mt. Komorebi, or even another city world, I’d probably keep most of my Sims there, but we don’t, so I just have to put them wherever they’ll fit. I’ll definitely try TwistedMexi’s Create-a-World when it’s stable.
I’ve recreated a few buildings from the series. Yugi’s grandfather’s game shop is the most obvious one (and the most challenging so far - that roof ?), but I’ve also built my interpretations of some of the other characters’ houses based on the few times we actually see them. If it’s a larger building (e.g. the Kaiba mansion), I‘ll check the gallery first to see if anyone else has built it - but most of the time, no one has. Apparently, every other Yu-Gi-Oh fan/Simmer on the planet is about as confident in their ability to build Pegasus’ castle as I am in mine. ?
The point I’m up to right now is about two years after the end of the series (Yugi and his friends are about 20 now), and since there’s no epilogue, I have complete freedom to do what I want with the characters’ lives. It’s roughly 50% headcanons, 10% limitations and 40% “hey, why not?” (*glances at all the aliens I’m saving for later*).
When it comes to shipping, I usually decide who’s going to get together in advance if there aren’t OCs or townies involved, and I’m not above using cheats if they autonomously do something that could mess up my plot. ? I might just let something happen if it’s in character, though.