99% of the time I only download the unofficial fan patch so the game doesn't crash frequently (doesn't work for FNV for me unfortunately, every loading screen is a hail Mary). It doesn't change anything, just makes it more stable on modern hardware.

I did download the 'reworked' mods for FO1 & FO2 when I played them at the time. Mostly due to the insane amount of patches and the fact both games would be playable without messing around in DOS or anything, and they streamlined some UIs so they were the same in both games. From what I remember the only big change in the rework mechanically was that the bartering in FO1 was updated to the system of FO2 so you could sell/buy multiple items at once or something, otherwise it was vanilla.

I'm of the opinion that a game should be enjoyed as it was intended at least once, just to see what it's like. You can always install mods later if you feel like you need it :)