As with so much in life, I find, the most difficult thing in writing a piece of music is to get started. I have been playing for some time with tools that can generate, to a greater or lesser extent, streams of notes which are created and controlled by varying rule setting methods.
This piece started as an experiment using Noatikl which I have had much fun with and recommend you have a play with if you like programming type toys. So far it seems very promising as a tool to provide the base from which to start constructing a piece. The best way to use it, it seems to me, is to set the rules to something interesting, try and retry until it seems to be about right, the let it do what it is built for, to iterate until you have a piece that suits as a basis for development, then capture the output as a Midi stream into Logic or similar.
Once you have the Midi output from Noatikl, the other 90% of the work remains with a fair bit of jiggery pokery, chopping and changing, assigning voices and instruments, and then endless mixing, balancing and fine tuning.