The book Slubber linked to is BRILLIANT, has all the recipes for every size and gluten/egg/dairy-free combo for both sponge and fruit cakes. It also has masses of instructions on modelling/RI/stacking tiered cakes, etc. It's invaluable and I recommend it to everyone who's beginning cake decorating!
The only slight criticism I have is that the sponge cake quantities are a bit over-generous but I tend to make any extra into fairy cakes for me to eat while I'm on my own the DCs.
My essential piece of kit in addition to what Slubber has suggested is a small non-stick rolling pin and board for doing all the fiddly cutter work.
Feel free to nick any of the ideas, I've adapted a fair few of them from ones I've seen other people do anyway
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Teaching yourself is the best way to start imo, I did (my first ever attempt at a cake is on my profile here I think), then enrolled for an evening class to get me away from 3 small dcs and that was great for learning new techniques like royal icing or different ways of doing things. Basically, the more you make, the more quickly you improve so everyone I knew got a cake for the flimsiest reason at the beginning
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