I have tried a little of this and know how difficult it is, so if this is your first attempt...wow! well done.
I found some very good info in some landscape books I bought by Joyce Becker. Nancy Zieman & Natalie Sewell have a book called Landscape Quilts. Gloria Loughman has one called Luminous Landscapes. Rose Hughes has one called Dream Landscapes, and Valerie Herder has one called Points of View. Joyce Becked has a DVD as well, which is very helpfull.....I haven't had the time or energy lately to really get into this but really admire landscape quilts......you are doing just fine..