My friend and I got volunteered to do cakes for our church's next social. expecting 200 people. was thinking of doing like 4 sheet cakes with different flavors. Questions: what size pans? how much batter? any good recipes? when can we start cooking, event is on a sunday at 1pm. Any help would be greatly appreciated!! 
A 12x18 single layer sheet, when cut into 2x2 pieces, serves 54. So for easy math, assume 50 pcs per cake. This equates to 4 of these cakes for 200 servings. If you're going to cut them into 2x3 pieces, then each cake will serve 36, so you would need 6 of these cakes, which will yield 216 servings this size.
I use 3 Betty Crocker cake mixes for this pan (grease-only-no-flour; baking strips, 325 degrees). I also don't use flower nails or heating cores and they rise and bake just fine.
When I price per serving, I price it according to the number of pieces the cake is designed to serve, NOT the number of pieces the client is going to cut from it. So no matter if they are cutting 2x2 or 2x3, the price of the cake is the same! If they are going to cut it bigger, then they need to order and pay for the extra cake.
When I'm doing a wedding, I bake/ice/decorate the cakes on Thursday. They sit on the counter until they are delivered to the wedding on Saturday. If I bake earlier than Thursday, I wrap in saran and freeze them. They only take a couple of hours to thaw enough to work with.
Hi and Welcome, rambem00. 
Here's a list of CC acronyms:
For a timeline, here's a link to Sarah Phillips baking911.com wedding cake help:
http://tinyurl.com/y2kcl8
If you have use of your church's kitchen, you might be able to bake the cakes and make the frosting one day and decorate the next...
Wilton cake preparation and servings guide for 2" cake pans:
http://www.wilton.com/cake/cakeprep/baking/times/party_2inch.cfm
If your oven is large enough you could make 2 layered 14x22x2 kitchen cakes for a total of 198 servings (party size of 1-1/2x2x4.)
However, a 12x18x2 kitchen cake would yield 108 wedding servings of 1x2x4.
If you only wish to make one layer sheet cakes - here's indydebi's guide to cutting and serving:
http://forum.cakecentral.com/cake-decorating-ftopict-302303-.html
The WASC cake is a great recipe and makes a large amount of batter:
(a tad over 14 cups using DH white cake mix, which is the perfect amount for a 12x18x2 pan.)
http://tinyurl.com/2cu8s4
HTH
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