I have a heavily modified Fallout New Vegas with tons of new items (mostly weapons and three or four armours) and it worked just fine.
http://newvegas.nexusmods.com/mods/47632//? I'm gonna try this now.
Project Brazil was kinda short. Maybe I missed something BUT: Very well made Vault, very detailed and I got lost once or twice. The storyline was enjoyable too and I liked the idea of that dream. Character voices are done pretty well, especially for a mod. There are some bugs and moments where there is text but no sound but I'm completley ok with that. One time, someon lost a close friend I think and the voice actor was not that convincing, I had to laugh but rest assured, this only happened once or twice.
Other than that, I did not want to explore that outside world until there are some quests in it. I don't want to spoil it for me. The part I saw was pretty solid apart from usual plants and trees hovering from time to time but the main game has the same issues and was done by professionals. All in all, I can say I really look forward for the second installment.
The bug with Dr. Rossman was my fault, I simply did not install that DLC fix. Well, I thought I had it installed, but I did not actually.