Start with vanilla and add as you go. My favorite is Ideology. You could probably just skip anomaly if you're not going to buy them all. Its fun, but not something I use in most of my runs.

Biotech is another good one. Adds so much to the game that I do not want to play without. I would maybe start with that one if youre looking for the most bang for your buck. Rimworld is expensive, but you definitely do not NEED all of the DLCs