I am making a square wedding cake with offset corners. I need around 225 servings. Does an 18 - 14 - 10 - 6 sound right? The 6 won't be served. Also, is there any secret to getting these off-set layers at the correct angles? Thanks so much for your help!

Do you mean like this one? http://cakecentral.com/gallery/1943509 I keep cake dummies in various sizes so I can play with angles, sizes when I am doing a cake. It also helps brides visualize the size of their cakes.

The 10" will slightly overhang on a 14", and the 14" needs to be on a 20".

Here are the right angle measurements:
4" 5.66
5" 7.07
6" 8.49
7" 9.9
8" 11.31
9" 12.73
10" 14.14
11" 15.56
12" 16.97
13" 18.38
14" 19.8
15" 21.21
16" 22.63
17" 24.04
18" 25.46