Usually when you redo the transom coring, you plan to lay in a couple of layers of 1708 to beef up the transom skin. Laying in the 1708 usually includes grinding the inside transom skin and about a foot of the inside hullsides and inside bottom. You can fill in the voids with layers of 3/4oz CSM (chopped fibers) and then cover with the layers of 1708. Lamming the 1708 to include the hullsides and the bottom creates a complete tie-in and makes the transom really strong. Then you start adding the coring, using fillets of thickened resin at all the corners, to include where the transom meets the hull bottom. You seem to have cut the stringers back enough to allow for this.
If you need more info let me know.  There are a lot of examples of doing this.

There are two significant voids in what appears to be the factory outer skin. What do all of you think I should do:
    1. Put a matching size piece of Matt in the hole
    2. Smear the peanut butter mixture in it
    3. Proceed with Coosa as if the voids do not exist (what I want to do)
    4. Something else

Which number

Here is a nice looking Explorer for what they're asking.

i am not good at posting pics

If replacing the fuel tank with a poly tank, then no foam is used per manufacturer requirements to allow for expansion. Only straps to keep it in place.
If your tank is aluminum, not sure what USCG requirements say, I always assumed foam was optional in this case as long as the tank is strapped down good.