I think you have the right idea. You're trading a minimum set of requirements for a better service. Your value added proposition is, availability. You'll always be on call if necessary. I typically ask for 20 hours a week minimum between 2 projects. This takes a little pressure off to spend time in the code base and iron things out. My contracts are typically 3-6months. Rates also vary between w-2 and corp-to-corp. Freelancing is a very inexpensive proposition when add up how much hiring and employing someone really costs. Hope that helps. Freelanceswitch.com is a great resource.