I feel like I could use some reset in my Skyrim. I didn't know I would hook on mods that much when I first got Skyrim. So probably I did all the steps wrong. Placed it on the program files. Used NMM to carelessly download mods (not anything game changing though).Which resulted in some unexpected results. I want to reset the game and do everything right this time for modded gameplay. I also want to save some characters and not being have to download all the data from Steam again if possible. (I am at vacation so limited internet access).

Follow the STEP guide for creating a vanilla Skyrim.

In the future, do not use NMM, use Mod Organizer, that way you will never run into this issue in the future. The STEP documentation also assists with learning MO.

Google search: Make_Skyrim_Vanilla_Again

Lookup STEP Project to learn about using MO and learning how to install mods in the correct order, the nice thing about MO is that since everything is built at runtime, you can change mod orders without having to uninstall/reinstall mods.

The only way I have reset Skyrim to vanilla is to rename the Slyrim directory to SkyrimOld, and then use Steam to verify the data cache. Steam will then re-download the whole thing again (5 Gigs). Then I made a copy of the vanilla Data directory, so I could restart again without having to download it again.

I have heard, but never tried, that you can speed up the download by just deleting all of the files and directories in the Data directory except for the vanilla BSA files. That way Steam won't have to download those again, which is most of the 5G.

You can try this by renaming your current Data directory to DataOld, create a new Data directory and then copy the vanilla BSAs from DataOld to the Data directory. That way, if it doesn't work you at least have the old Data directory around, and if it does work, you can easily copy the SKSE directory over, the USKP files, and any other mods you want to keep.

I would ONLY recommend this though if you are computer savvy enough to know how to manipulate files and directories in Windows Explorer.