Referencing both a node and user in the same field
There are a few ways to do this. You said "and/or", you could use Field Collection and add a node reference and a user reference to it. See the field collection module. 

The other option would be the relation module or the entity reference module which can both reference any "entity." The former is a lot more complex. Entity reference has a usable widget with autocomplete which might be exactly what you need. To narrow the entity reference down to the exact content types you want along with users, you will probably have to write a custom widget. You can see the default widget implementation in the source.