I would say you'd be better off getting started now.
Not only will this benefit your business from a marketing point of you (could never hurt to get a head-start), but it'll keep you focused. If you're just keeping your plans and goals to yourself and you begin to have second thoughts about it, who's gonna stop you from quitting? If you communicate with others, you will feel accountable to them.
Also, blogging can help with your planning. When you share your ideas, you might get some good suggestions, too.
I think you're more likely to stick with it and be successful if you get started early.