Be sure to follow the instructions on the 4GB patcher mod page as this patch cannot be installed with a manager. To counter this, download and apply the 4GB patcher to your Fallout New Vegas executable (FalloutNV.exe in your game folder). However this makes it prone to crashing due to running out of memory. Install and run MO2 - almost all future modding and loading of the game must be done through your mod manager to ensure that your mods are loaded when the game starts.
The recommended manager to use is Mod Organizer 2. This generates some necessary configuration files for the game to run properly. Preparing Fallout Who Vegas From a Fresh Install
Due to the age of the game and the advancement of computers since then, there are several essential mods and tweaks required before the start of a game in order to ensure a stable and (relatively) bug-free experience. This page will cover how to install Fallout Who Vegas on a fresh install of Fallout New Vegas.