Fallout New Vegas can generally handle around 130 mods but this varies from system to system. For instance on my old PC, my limit before things in game went crazy was 130 but with my new laptop its 132.
For increasing plugin limits, while the hard cap is at 140 (This includes base game and DLC as plugins) the best option is to use a plugin merger. I like to use this one: http://www.nexusmods.com/skyrim/mods/69905/?
Don't worry I know it says Skyrim but it explains how to use it for all Bethesda titles. Essentially with that you're just doing what the title entails, merging esps together.