Is lua.org a good place to learn scripting?
Not for ROBLOX. Lua is a language used by ROBLOX, but ROBLOX has made it so they use their own codenames for everything. You would find some things that would work with ROBLOX there, but you would not learn how to make a game with ROBLOX there.
For Lua yes. But its not rbx.Lua witch roblox uses. But you can do what I did and learn Lua THEN learn the roblox api for Lua :)