Practicalities: Do you have insurance? Will customers be coming to your house and will you need insurance to cover that? How are you packaging them? If you are using your car to transport the cakes will you need business use on your car insurance? Let your house insurers know you are running a business from home.
Pricing. Seeker didn't emphasise its importance nearly enough
Make sure you have a niche. Something different to offer than the rest because it is a horribly saturated market right now everyone seems to be doing it. As long as you can stand out from the crowd you should stand a fighting chance.
Do not underestimate your pricing either, and don't forget to factor in your time spent actually making the cakes and charge accordingly for that too. Seen so many people say "oh yeah, can do that for £30 no problem" and end up spending half of the day in the kitchen and be lucky to pocket £5 from it.
I did the whole cupcake thing when it was just starting off a few years ago, went great for a while, but people get bored and its hard to keep repeat customers for things like that. Most people see it as a very rare treat so you really have to reach out to drum up new business to make up for people not coming back for more each week.
I stopped the cupcakes when i went back to work after maternity leave a couple of years ago and quite frankly I was sick of the sight of them now I just do celebration cakes for family and friends when I can as a hobby, and bake for fun. Much more enjoyable.