Hi charwork.
First of all......This is a very ambitious first level.

Alas....I could not play it.
I got the dreaded
Memory Access Violation when I tried to open it. SO......
I put in the editor to see why. WOW!!! Loads of stuff! (Sad to say-Too much stuff!)

So I edited it and took out all the extra "stuff". You can only have up to 100 of an item. So I had to remove alot of trees and patterned floor tiles. Still couldn't get it to work. Then I changed all the moving walkways to just plain floor tiles. Success!
THEN....
I noticed you intended to use LnSCastletown and popo3dslide. Neither of which showed in the level. Castletown is a CustomModel, not a CustomHouse. When you intend to use a CustomModel you have to use the ABCD squares in the editor A=model1, B=model2, etc. And place them as you would when you place a house.
You also need to either post a zip file with the CustomModels in it with your level, or specifically say which CustomModels you used so people know what they have to download.
None of this is meant as criticism. Believe me, I learned the hard way! Trial and error and error and error!
I did enjoy the level once I could open it and if you can't figure out how to use the CustomModels , let me know and I will try to help!
jg
PS: Oh Yeah! Welcome to Wonderland!