Let's create a list of milestones here.
For each of them write:
- How can I tell this part is finished?
- What needs to be discussed/agreed on?
- What needs to be bought/found/acquired in the course of making this?
- What needs to be built/programmed/grown/written?
Risks and Plan B
- Is there anything likely to go wrong?
- What can we do about this in case of unexpected difficulties?
- How long will this take? (Workdays/Weeks)