The earlier you write your scope of work, identify required materials and submittals, and make your schedules, the smoother your job will run. the delay of these will only give you unnecessary headache and you will have to do this anyway at some point regardless. So better do it now than later. Spend a lot of energy trying to build the job on paper, spend as much time as you can, before it starts to get build in the field. The preconstruction phase is very, very important.