Some methods are unavailable at the moment. So, no, not any Lua script will work at the moment. The methods that works are the ones that aren't commented out in the Method script files. I did a big update the other day, which includes a lot of hooks that are now available to use, here's the script with all the working (some are untested) hooks. http://pastebin.com/J1WTs3MC.
If you go into UnitMethods.cpp or any of the other method files and you see a method with commented out code, that means the method is probably not working.
I wouldn't say that. Gossip works fine. There's only at least 15 (more or less) methods that aren't working right now. A teleporter will work just fine. I don't know about Transmog, because if it uses DB queries, we don't have that setup just yet.
I took Deputy Willem (entry id = 823), the starter quest npc for humans and duplicated him. The duplications entry id is 900(,)000. I changed LOCAL NPC_ID = 900(,)000 in the .lua file. So far, it doesn't work.
Initializing Scripts...
2013-11-30 21:34:18 ERROR:Scripting library not found or not accessible.
2013-11-30 21:34:18 ERROR:Eluna: LuaEngine is Disabled