Should I leave my job to set up in practice?

My apologies in advance for the lengthy writing, I need to outline my current thoughts.

I am considering leaving my current job to set up a practice working from home. In the medium term this is where I want to be, I want to be my own boss and I am extremely happy with the decision. In the short term I am unsure as to whether now is the best time.

I am currently in secure paid employment for a decent salary, halfway through a one year contract which I expect to be renewed. I am on a three month notice period. The problem is that I don't particularly enjoy my job and believe that my time would be far better spent working on my practice.

I have mainly worked as a management accountant and there is a lot I need to learn in order to become a good accountant in practice. I am currently working through this by reading this and other forums, internet research, working on friends/families accounts etc. However, I have to do this in my free time and I believe I could do a much better job if I was spending all my time on this. I also expect marketing to take up a significant amount of time in my first two years.

I don't want to deceive my employer by combining both jobs but I have the typical accountant's risk-averse outlook on taking a big step into the unknown and wonder whether I should build up my client base first before handing in my notice.

I would appreciate any advice, particularly from people who have set up recently themselves.