With this mod specifically, I don't think it matters which comes first since it does not have any link with the main story. This mod is only the first chapter so unfortunately, once you've finished this mod, you'll have to wait for the next chapters before you continue your game. You will basically load your saved game after chapter 1 and continue from there when chapter 2 is released.
I found that although some of the texture mods do make the game look pretty-er (looks pretty good standard), it does make it pretty unstable. Unless there is something specific that you want modded, I'd recommend going vanilla since Fallout 3 and Fallout NV can crash quite often as it is (no additional help needed).
P.S. This is a VERY long game. Probably over 80 hours. I think I played it twice. First without DLC and then with DLC some time later.
http://raptr.com/ViperGTI/games?sort_by=hours_played