working with WPF usercontrol and MVVM

Question

I have following questions

1. Should the consumer of my usercontrol assign the usercontrol's DataContext or set some dependency property. (related to #3 : if DataContext then my individual items need to bind directly to the object given in DC, if DP then I have the luxury to have bind to any VM)
2. If they set property, and if I am using 3 primitive items, should I accept them as individual properties or combine them together to a Model for my usercontrol
3. Should I ask the consumer of my usercontrol to send me model or viewmodel ( I say viewmodel but for all the controls I have used so far, I have never seen anybody asking me to send them VM - I am sure some could be implementing MVVM internally