If you used nmm to install the mods, you can via nmm remove the mods from the game with out deleting them and there for having to down load them again when you want to put them back in.
If you used nmm, open the program and look at all the mods. when you click on each one on the right side it will open a mini view of what is posted and nexus about the mod. Read that and look for any incompatibilities and compare that with the other mods you want. If you find an incompatibility between 2 mods, you will have to choose which one you would prefer.
When installing mods via nmm, it will let you know if you are overwriting a file and from what mod the file is from. For example, I have a couple face change mods, luscious lips wants to override pretty face's file for the lips. The pop up lets me decide yes, just this mod (meaning pretty face) everything (meaning any mod and any file regardless what it is) or just this file or no to the same things. Because I want to see what all it will overwrite I never select everything (sorry if I don't have the right words for the message that pops up but you will understand when you get there). This way you can pick and choose what exactly you want from this mod, I.E. yes over write pretty face's lip file but wait a minute, why are you overwriting bla bla bla?
Load your game, make a "new saved game" and exit the game. Now start NMM and remove (not delete) all your mods. choose which ones are most important to you and load them first working your way down to not so important. That way as you work down your list is it easier for you to choose what you really want to install from this mod if the overwrite message comes up. Don't forget to run BOSS when done.
Hope this helps, I'm new to the game also
After typing all this I saw your "note" so no mods were installed via nmm. What I would do in that case is remove all the files you put in the skyrim directory. If you don't remember, reinstall the game.
on the nexus web site, across the top it says "install NMM (0.45.7)" install that or click the link I included. Now when you find a mod at nexus you want, a little below the pictures of the mod select "files", on that page you will see green bars with "download with manager" written on them. By clicking that it will start NMM on your computer, download the file, and put it in the right section.
The mod is not installed yet so follow this. click the link to the left and it will bring you to "climates of Tamriel". You need to read through the description and pay particular attention to anything that tells you, you need mod abc, and xyz for this mod to work, also pay attention to incompatible mods. Sorry "climates of Tamriel" is a bad example because it does not list any. continuing on, select "Files". You will see 3 sections (main files, optional files and old versions). In the "main files" there are 2 available, only one has the "download with manager" available, since they are the same version, and the same date, click the download with manager (only if you want this mod, I'm only using this to show you how to download from Nexus). If NMM on your computer was not running, it will open the program and start downloading. When it is done it will put it in the right section, but where? Environmental, climates, patches etc. scroll up on the web page and underneath where you see " Climates of Tamriel - Weather - Lighting - Audio by JJC71" it says "Skyrim >> overhauls". Now we know NMM will put it in the "overhauls" section. Expand the overhauls section and there it is (you will also note, NMM also puts a blue number to the right of the section that has new mods just downloaded), but it is still not installed. Select it and on the left click the second from top button, it looks like a blue puzzle piece with a red arrow pointing to the left. After installing if you are using SKSE, what I do is start skyrim normally (none skse), on the intro screen select data files, close skyrim, run BOSS, then start skyrim via SKSE.
That's it, your mod is installed and easily removed if needed.