Being able to work without supervision isn't an ability that everyone has. I have had several run ins with people that would love the idea of self employment but when it comes down to sacrificing free time to get it going, it just never gets off the ground.
For a written plan, so long as you outline what you expect from him, by when and highlight what compensation he is entitled to if he meets his end, and conditions for termination.
If you are thinking about the comission sales end of thing, there's many templates available that you could customize.
Here's one I found quickly as a reference:
http://www.biztree.com/Templates/Commission-Sales-Agreement.html