I am making a 10", 8" round cake with a basketball cake from the Wilton sportsball pan going on top. My questions are:

1.  Is it necessary to put cardboard in between the two ball pieces? Or is the frosting enough? Will it keep it's ball shape or sink? Does it need to sit on a board, or can it go directly on top of the cake?

2.  How should I stack it? Use a dowel rod through the whole ball, or just put the cake on a small board and use dowels in the cake below?

Thanks for the help.

generally every 4 to 5 inches of cake (from table top up of course) needs to be boarded and doweled for the cake to be secure and stand -- so yes the ball should be on it's own board -- use a center dowel if you want to guard against it sliding -- probably a good idea in this case and deliver it cold from the fridge -- in fact i might use a couple skewers in the ball angled out for the best hold on it x 

best to you

Thanks!

but it still needs support dowel that goes straight up and down from board to board holding/supporting each tier including the top tier (aka the basketball)

the x skewers are just to provide a bit of stability for the top tier