in one side
<Ideally, I would like to be able to easily texture this creation with a different color for the body, face, and various colors for the spikes
in another side
<Originally, I had selected the entire model and ran a boolean union command so that I could fillet all of the pieces
seems that is antagonist with the 3ds format ;)
So solution is the Michael obj tip;)

Else you have always the rustic solution of particular selection of polygons in Sketchup!
The different "help of selection" + "hide selected" make easy choice for paint any aeras ;)