A very basic sponge recipe for about 12 fairy cakes is 4 ounces each of caster sugar, self-raising flour and butter, and 2 eggs. Dead simple to scale up for as many as you like. Add vanilla essence for plain ones; for lemon ones, add the grated zest of one lemon and a bit of the juice; for chocolate ones, replace a tablespoon or so of the flour with the same amount of cocoa powder (not drinking choc!)
There are other recipes for more chocolatey ones with real melted chocolate, but if it's basic you want - these all work fine!!! Icing wise, I don't know really. The ones with egg white in would be very hard once set, and I'm assuming you'd need some sturdier ones at the bottom?? Maybe you'll need more than one kind of icing - you could have the gooey ones at the top then!! I make a frosting with 6 ounces of icing sugar and 1 ounce of melted butter and a few drops of milk. Beat or whisk it and it's lovely and fluffy, but once chilled a bit, it's a bit firmer. Not suitable for your foundations though!!
One other bit of advice is to build it in stages and let each one harden before you start the next. I've done it with cornflake cakes before and it needed a good solid bottom!!
Have fun!!