Here's the key idea for understanding Pitbull 4: You create and define any number of unit frame templates, and then apply those templates to the various types of unit frames used in the UI. So, for instance, you can define a template called "Character" (or whatever name you want) that displays a certain size, uses a certain kind of portrait, has these bars with this text and buffs here or there or no buffs at all. THEN you apply that template to the "Self" unit frame type, and your character's unit frame will possess all those properties.
If you want your Target unit frame to have a slightly different set of features you simply create a new template (I would just copy the one you create for your character), give it a new name, and make the changes you need. I do exactly what you're trying to do: my Self unit frame and my Target unit frame look very much alike, are approximately the same size, carry most of the same information except the Target has a cast-bar, and only the Target frame has buffs and de-buffs. I do all that by having two similar templates and tweak the minor differences.
Once you have your second template ready you just apply it to the "Target" unit frame type and you're set. The great part about using templates is that you can then re-use that same layout for other similar unit frame types. For instance, my Focus unit frame uses the same template as my Target frame, so they display exactly the same set of information in the same way.
