First time modding fallout 4 on pc, what's essential?

after the version check, my four that go in before anything else: F4SE, Address Library, Buffout 4 and the Unofficial Fallout 4 Patch. most bigger mods list some of them as requirements anyway. install those, make sure each matches your game version, launch once to check it runs, then start adding the fun stuff a few at a time.

Check your game version before anything else. The next-gen update broke a lot of older mods that rely on the script extender, so make sure each mod lists support for the version you're actually on. Plenty of people downgrade for that reason. The base everyone starts with: a mod manager (Mod Organizer 2 or Vortex), F4SE, Address Library, Buffout 4 for crash fixes, and the Unofficial Fallout 4 Patch. After that you can add QoL stuff like Full Dialogue Interface so you see the actual lines instead of four-word summaries.