I've been pretty satisfied with this modlist, give or take a couple of mods depending on preference: https://nexusmods.com/fallout4/mods/23556/. Photorealistic Commonwealth is the ENB I spent the most time with but the DOF is so strong that you'll likely have to disable it for combat scenarios. I recently switched to Decent ENB, which I really like because it is much closer to Vanilla FO4's bright color scheme but so much crisper and better looking with very little impact on performance. Decent's DOF is light enough that I haven't had to disable it at all, even when in combat.
I know its not a spiral staircase, but I have a good solution for a staircase that takes up one square when building with the warehouse or factory set of building tiles.
Use the small, metal staircase and attach the two small square floor to it then use another small staircase to complete the run to the next floor.
Here is a sketch I made to try to illustrate what I mean.
https://photos.google.com/photo/AF1QipO1fLIcR9i-LcjrQ18MbNaT8cF7uNByfjjFH9ms
Sorry, I'm at work and can't show you what I mean in game. LOL
Watch Gopher and GamerPoets' Mod Organizer 2 tutorials on YT. It's the best mod manager and the most comprehensive explanations you can probably get. Gopher's videos are based on Skyrim but everything works the same way in FO4. Mods come from nexusmods.com for the best selection. The only thing that's really different for FO4 since release is the .ini tweaks that need to be made to enable mods, but MO2 uses its own .ini files that already have the relevant changes included.
VPNs are your friends. Investigate them. Use them. Love them. They will love you back. I recommend Private Internet Access, but there are free VPNs that will help you as well.
Try Settlement Limits Slashed. I've used it for a few days on my xbox and so far I haven't had an issue. I've built the ever-loving shit out of Red Rocket, I would guess at least twice the vanilla limit, and it's running just fine. Just a head's up though, it doesn't work in DLC settlements because the modern hasn't gotten most of them yet. Also, I never got the notification saying it was working, it just worked the minute I loaded my last save.