There are so many interesting mod, I think if I take all mod which I like, the list will easily exceed 100.

Is there maximum number of mod I can run?

If I run too many, will my game become very lag, hang or even crash?

After googling your question, the limit is 254

255 is the max including Fallout.esm. I believe every plug-in, including official DLCs (Dead Money, etc), promo pack (Mercenary Pack, etc), patched plug-ins (merged patch, etc) and all mod files deduct from this number.

The more mods you run, the more data is crunched. Depending on the mod in question, this basically results in longer load times on start-up and between cells, and increased lag and lower frame-rates. High resolution texture replacer mods, for example, can definitely cause a performance hit. Instability issues and CTDs are more commonly caused by sloppily-made mods and conflicts between mods.

Learning FNVEdit and Wrye for conflict detection and resolution, and for merged/bashed patch creation is ESSENTIAL.