I found a lot of mods that make thinks lighter, and add mark and recall, and a basement I like. They are all on Steam, and what I want to know is if I can have too many? Will they all work together? Or should I just leave them alone?
The number of mods Skyrim can handle seems to be limited by an unsigned byte, meaning slightly less than ~256 mods. (this account says 252 accounting for Skyrim.esm, the Update.esm, and the Saved game)
Oblivion and Morrowind where limited to 255 mods, so we could assume that Skyrim have the same limit too. That said, 255 is still a rather high number, so unless you're grabbing every mod you find, you should be fine.
As for compatibility, it really depends on the mod and the load order. Some mod may work without problem, others only in a certain order, and some others just won't work together. It is a case-by-case problem, so you should carefully read the README of the mods, and you should try using tools such as Wrye Bash and BOSS to keep them organized.
Only subscribe to dynamic and constantly updating mods. For example, the dovahkiin hideout or midas magic, which keeps updating.
But for something like the paarthurnax fix or perfected weapon mods (that require no more attention), you unsubscribe but keep the data files so they remain in your skyrim but are no longer 'subscribed' as such.
Strictly speaking, there's no such thing as 'too many' per se.
However, mods can conflict with each other, and some do expand the demands the game places on your system (I.E. texture packs).
Other than known or obvious conflicts though (you DO read the README, right?), all you can do is try them and see. If you have issues after installing a bunch of mods, disable them one by one (or the reverse) - its really the only reliable way to troubleshoot.
I am using NMM and i can't run more than 255 mods, when i select 256th a msg appears that you can not use more mods. So i am currently running 255 mods with NMM..
But you can run as many mods as you want which don't need install (means the mods which don't have esp or esm files like the textures, sounds, meshes like stuff)