Application Flow
The flow can easily to explain how the system work. Also can provide better example for developer to discuss and develop. I would base on the main user flow to create flow chart than present for client.
Wireframe
After the system flow confirm. I can go on to create wireframe to provide a visual outlook for whole system.
Wireframe is a important part for the whole design the draft look make everyone see what would be happen in the final delivery so that's would reduce the risk of extra cost for development.