Lua & speed

Hi I am doing a managment game like roller coaster tycoon and I want to allow powerfully addons system ... so the best solution is to have a scripting system. I want to do a lua scripting system that define buildings comportment I mean the game engine will call same fcts like OnSelect or Update and these fcts will be implemented in a lua script. It is very easy to add some buildings and very powerfull but I wanted to have some information about speed we just have to compile the script at game startup. But, each frame some part of the script will be executed like Update fonction and we can have a lot of buildings in a map. I don''t now yet how lua works internaly so I have no idea of cpu overhead. thanks a lot! and escuse me for my poor english ...