I am planning to merge all armor/weapon/clothes mods into one single esp.
There are about 120 of them. Is it too much?
Should I merge them in several esps? Will this be better for performance?

Nope, that's perfectly fine. Just keep in mind you can't do that to an existing game without losing content on them all in that save.

How it helps performance I guess depends on how detailed the content is. It'll free up 119 slots, and may help with disk access, but I wouldn't expect miracles otherwise.

Thanks, Arthmoor.
You are the first man to answer a question of mine for the last 3 days. I suppose everyone is busy

Since the last few day, i saw very very low activity on the forum... normally, when we create a post, or a new thread, after 10 min - 2 hour, we need to go to page 2 since so many people responded in other thread. Now i look at the forum... the same 10 thread stay at page 1 for like 9 hour... not normal.

Old game is old and a lot of us are now older with different lives than before. So yeah, more dry spells here an there..