I have 8" SPS plates but need to do a 9" tier. Can I safely put the 9" cake on the 8" plate or should I buy a 9" plate? Thanks!
Yes you can. If the cake needs a border put it on a 10" board; otherwise use a same size board.
I have put round cakes on sq plates; sq cakes on round plates and cakes as much as 2" larger than the plate
Yup, what she said!