If Model is having a DynaField and PageFlow ModelLink and if DynaField is scoped by PageFlow, then instead of regular DynaField, individual components of DynaField are available (defined for the PageFlow) and the Administrator should be able to drag and drop the individual fields just like any other field. If no components are defined for the PageFlow then no fields will be available for the DynaField.
This will work for Child Model Level (grid) as well provided both DynaField and PageFlow defined on the same level.
By default requiredness defined for the component as defined in DynaField definition is applied for an individual components, i.e. Required or Optional. If required Administrator can override the default mask using the action mask feature of User Defined Pages.