HELP!!! I'm panicking here

I just got an order to do a 3D tractor cake for this saturday. I have never done a 3D cake before....other than carving a fist for one of my cakes. It's not that I don't think that I can do it cause I rather like a challenge. But she didn't leave me much time to get all my info together.

If any of you have done a 3D tractor, I could use your help.
Questions:
1. Can I use WASC recipe for carving?
2. How to have the tractor elevated so it's just the tires touching?
3. What to use for the tires? I'm thinking RKT
4. How do I know how many servings I can get from this tractor? I know that depends on the size pans. It's for 20 people and I was thinking of using loaf pans for the tractor and have it sitting on a 9" square cake (maybe).
5. Help if you can!

I just did one last week and used rice krispy treats pressed into a bowl and covered with fondant. I let it dry overnight then put toothpicks into the rkt and pressed into the cake worked great. Mine wasn't elevated. I used the 11x15 pan cut into 3 equal parts stacked 2 5x11 then the 3rd I cut in half and stacked for the cab. Then I rounded off the front and frosted with buttercream and added fondant windows, tires and John Deere plaque. Oh for the pipe I used a straw wrapped in fondant. It turned out really great. I wish I could post a picture but not sure how for my computer won't let me download anymore but there are several in the galleries. That's where I got my ideas. Hope I didn't confuse you.

Thank you, I wish I could see a picture of yours. I've been searching the galleries and may have to pm some people. That is a good idea to use the larger pan and then cut. Do you know how many people that served?

I saw a cake somewhere (can't remember where!) and the decorator had used those doughnuts that look like tractor tires (crullers???) dipped in chocolate. They looked really cute.