I don't have a cake business, but I do have a successful internet business. There is way more to it than you might think, from deciding on your business structure to licensing, annual reports to the government, book keeping, invoicing, the list goes on and on. Honestly, I don't think I could ever make money at cake in my town. I think the very best advice given is to know your market. People won't pay more than $200- $300 for a large cake here. For me, that comes out to less than $10 an hour for my time + ingredients.
I would suggest a book keeping system such as Quickbooks. You can use it to track all of your expenses as well as invoicing customers. You can also accept credit cards with it though their fees are rather high. When it comes time for taxes Quickbooks will practically do them for you.
A website is very important and can be a large expense. You can go to www.wix.com and get a pretty nice layout for free. An added plus is that you don't need a background in HTML.
Facebook and Twitter can also be important marketing tools.
From strictly a business stand point I would recommend that you not replace your counter tops until you have proved that you can run a successful business.. They won't bring in any more money initially and will be a large investment. You would be better served to put that money into marketing and advertising.
I would also advise the purchase of a Kitchen Aid, I can't imagine the amount of work not having one would bring! I recently made a batch of butter cream by hand using a whisk (wasn't at home - no mixer), I thought my arm was going to fall off! haha