I have a mod im making which adds a fairly large vault to the game and will have a fair size quest line in the future. Now the mod is currently a .esp but the thought has crossed my mind as to whether it will need to be a .esm or have a .esm as well as a .esp to make it work more smoothly etc. My question is do I need a .esm or both a esm and esp and what advantage will it bring over a standalone .esp? I know esm files are masters and esp's are more of a file which changes things from the esm but that's about as far as my knowledge goes. This is my first mod so forgive me if its a noobie question that's very obvious to your self. The mod btw only has a 1 master being the fallout 3 .esm.