The default is Libraries/Documents/My Documents/My Games/FalloutNV/Saves unless you chose to name a different location at install.
Cloud sync wouldn't have the files if they were deleted since its purpose it to allow you to play across several different PC's. If you delete content, it syncs up and would have been deleted there as well.
Deleting all local content should only remove the game files, personally I've never seen saves removed by uninstalling a game on Steam.
As far as using a cheat to level up, you can do that, but you'll also need to assign the Perks that would be appropriate for that and the earlier levels.
Here's an article on
GamesRadar with a number of different builds and associated perks.
Typically, for any game I back up saves in a "Previous Games" folder and name the saved folder with the level and character type. That way if I feel like trying a different character build I can start a new game, but keep a character I liked in the wings to play at a later date when the mood hits me.