? on ordering birthday cakes

[a*lil*bit*goofy]

a) do only specific restaurants at WDW do this
b) how much does it cost, typically (ie to feed 7 people, 2 who are kids)
c) how far in advance must one do this (ie when i do my adr's at the 6 month mark, do i request then?)
d) do they precharge you or charge you at the table
e) do u have a choice in flavours

thanks so much!