I'm making a Hamilton (the musical) themed cake.  

I want to have silhouettes around the cake like this one

 and then the star silhouette standing against the top tier with the figure above, like this:

For the silhouettes around the cake, would you dry the pieces around a cake tin or keep them flexible somehow?

For the top silhouette, how do I support it? I have sandwiched skewers between cut outs before but I don't want to have to do 2 cutouts. 

Yes you can dry the silhouettes on a cake tin or styro round.  They won;'t stay flexible but will dry rounded a bit.   For the top one - maybe insert toothpicks or popcicle sticks in the 2 'legs' ? 

You can always use pastillage and let it dry completely.  It will be as hard as a rock.  If you cut out the silhouette from gum paste or fondant with a whole lot (A LOT) of Tylose and let it dry for several days, it should hold up.  You could always place it so that a bit more of the figure is supported by the cake tier, but still extending above it for the same effect.