Are you saying that the whole elevated block is from one mold? Casted in one piece? It looks great, at least in the picture anyway.
But I think, as you mentioned, to go to a more modular approch will have many benefits.
Not only that it will be possible to combine the pieces differently and give the opportunety to create several buildings. I an other advantage will also be for the production (casting) part. Smaller parts are easier to cast and even if you get a miscasted piece, a small one isn't that expensive.
Do you know already how to join the different pieces? Maybe you can do it in a way like the castle pieces from playmobil.
I like your work very much, go on!
Lurch