Attempting to make a my little pony cake- help needed

[kbaby]

DD is having a my little pony party and wants a cake. Instead of buying one I though I would make one. Now I have an idea in my head but not sure how to make it.

I thought about having a rainbow, at one end of the rainbow would be a big heart which I could write her name and age on etc and at the other side of the rainbow having some grass with a mlp on, for the my little pony I was going to find a picture stencil it and use it as a template.

Whats the best thing to make it all out of buttercream or fondant icing and also what cake tin shall I use to actually get me the cake shape.
Also do you think I should practice this first and if so how?
Help

how old is she?

It sounds like you're making it uneccesarily hard for yourself

I would make an oblong sponge cake in a roasting tin, ice it with green buttercream roughed up to resemble grass, sprinkle with sugar flowers, add the right number of candles and position her favourite ponies (or a new one - do they do a special birthday one?) cavorting on the top

or hire the appropriate number tin and decorate in the same way

or a generic pink fairy castle cake (add a pony by the front door) always goes down well

go and have a look at MaureenMLove's profile. She did a fab pony stable for her DD once

For inspiration or emergency back up see here.