In a detailed response account for the major differences between the book and movie thus far?

Well much of the background of the book is not explained in "Blade Runner". The whole off world-colony thing is not dealt with in detail. Many of the secondary characters in the book do not exist in the film. BladeRunner begins with Deckard and his task of retiring replicants. The book spends more time giving background to this dystopia before really picking up with Deckard and his task.