Multi-step projects and Monday Hour One

When doing the to-do list download, do you write out all the steps of a project and schedule each one? For instance, I want to update the irrigation at the preschool where I take care of the garden. I can write that on my list but it entails many steps. I don’t always know all the steps of a project in advance (research irrigation options, call the landscaper, create a proposal, send proposal, get approval, purchase supplies, coordinate schedule with landscaper, etc, etc). Should I simply schedule the first step, and any steps I know of? Or should I spend time (or schedule time) to research and lay out the plan and then add the steps the following week?