I don’t know if there really is a limit, but some mods may slow the game down. It also depends on the system you’re running. And the quality of the mods of course. I currently have about 130 mods in the mod folder, and the game runs as smoothly as ever. Of course I don’t have them all activated at the same time – some of them aren’t compatible.
That said, I don’t see any reason not to run the latest version of the game. You get more content and a better game. I can’t wait to play version 1.9 when it comes out. 🙂
Anyway, it’s your choice. Just be a little careful/smart when installing mods. Don’t just blindly activate a bunch of mods at the same time and expect everything to work flawlessly. Read whatever information comes with the mod, use your common sense and you’ll be fine!