Unfortunately, because of the nature of Fallout 4's performance issues, the Xbox One X's greater GPU doesn't help out very much, and the CPU isn't that much faster than the base Xbox One. So you'll get better performance, but don't expect leaps and bounds. Many of the same problems still arise.
In general, supposing you aren't running any other heavy mods besides Sim Settlements, you can pretty much run all optimized city plans with maxed out graphical settings. The only option that is disabled with the default "Xbox One X" setting is "Clutter", though you won't crash your game by turning that on. However, don't expect silky smooth performance.
In theory, building multiple city plans at once shouldn't matter anymore, because that problem was fixed a while back. However, fast-traveling in and out of settlements is the most likely cause of a crash. By approaching the settlement slowly, from a distance, it gives the console just a little more time to load in and out assets and can avoid hard CTDs. That being said, if you can't fast-travel into settlements, that's a good sign you need to reevaluate your load order.
I'm actually in the process of writing a long .. thing ... about using SS with the Xbox It's not finished, and I just broke my regular computer, so it might be a while. I can PM you the incomplete version if you like--it might have some useful information for you.