http://skyrim.nexusmods.com/mods/20801//? If you want to use many texture packs but be warned it can cause quite some performance issues. You should have at least 2gb of vram for that, More would be better.
Install your mods with the Nexus Mod Manager (or Wyre bash if you want a more complicated but more versatile option).
Also use BOSS to get the load order right and clean at least the official modules with tes5edit.
Also think about what mods you combine. 2 mods that change the same AI scripts are a bad idea, 2 mods changing the same textures are ok but only one will be loaded (the mod manager asks you if you want to overwrite files). Don't use textures which are for different meshes so if you install something that changes meshes watch out for that.
Sky UI is pretty much needed for many mods to access their config and its a better UI anyway.
Climates of Tamariel and Wet and Cold are nice for more weather and weather effects. Automatic Variants adds an option to use different textures for the same item or enemy type.
Depends entirely on the mods. Lots of graphical overhauls can reduce FPS as can a lot of scripting but in general the amount of mods does not matter. You could have 200 object mods installed with no issues for instance. Just try out a few at a time before going all gung-ho to make sure they work and don't cause too many issues.