Not a mod but I think SKSE is the most important since you can’t even have SkyUI without it

SkyUI

Open Cities

Alternate Start (there’s multiple different ones)

moreHud

Immersive Patrols

XEdit, it’s not a mod but I think it’s more important than most mods since

• it lets you make a lot of tweaks on your own
• there’s no point in having hundreds of mods if they override each other, so being able to make merged patches is critically important

Immersive Citizens AI Overhaul