My suggestion then is to just create the terrain now. Trust me, you will appreciate anytime you spend on it. I, for instance, have a very..... unique..... terrain to it. My TD is not flat and boring with huge wide open spaces, everything in it is very different.
Terrain is one of those things that is easy to fool around with to get a desired result, also you can spend a lot of time on it and it really shows off. Best thing about while you make the terrain is that, for the most part, it is easy to come to a 'stopping place' in it. As I am sure Ralle can back me up on this (and other maps makers), this does not hold true for triggers. I will put it this way: Shvegait (burbenog and mindblaster creator) and I have spent many, many, many nights until 5am trying to debug a single tirgger for our respective maps(did I meantion many?). It is NOT easy and it is very difficult and usually it is something that most players might think of as minor but actually has a large impact on the game.
As for helping you, I would gladly assist you if my schedule permits it.