I'm making a cake that needs to feed 45 people. I was going to go with a double layer 10" on the bottom & then an 8" double layer for the top…would this work or should I go with larger?

Ace,

The size of pieces of cake served will help determine the needed number of servings.  Cutting the cake pieces 1 1/2" x 2" and following the Wilton Servings Chart, the 10" should serve 28 and the 8" should serve 20.  That is a total of 48 servings.  

Hope that helps.

Christina

http://www.wilton.com/cakes/making-cakes/baking-serving-guide.cfm

I'd go smaller... 9x6 or 10x6 using wedding servings--8 cu. in. 1x2x4.

http://www.wilton.com/cakes/making-cakes/baking-serving-guide.cfm