Nexus mods are mostly cosmetic mods, reshades, or file replacements which the game will read as native files when you replace the originals so none should have any (negative) effects on steam achievements. Unless you have something specific in mind?

I was probably going to go for stuff like cosmetics, yeah. I haven't played through the game fully yet, so i didn't want to change too much of the actual gameplay. So stuff like graphics tweaks, or things that allow you more customization. Thanks for answering that though, i'll take a look.