I have Skyrim on my pc and I'm lookin to get Legendary Edition since I don't have any of the DLC. I have some Save files however that I would like to keep playing. Will those files still be playable when I get Legendary Edition?

Yes they will work perfectly fine. If you use mods make sure those are active when you load the save on the LE. Don't want any Skyrim script witchcraft.

Yes. All they do is add to the main game.