I'm a mining geotechnical engineering consultant, however I work for a multi-national consultancy.
I am considering starting my own one man business in probably 10 years or so. In that time I should have the required expertise (20 years experience) and the contacts ready to go.
The key issue for me is to build my contact network so I don't have to go and actively market myself to mining companies. In my industry, once you are well known, clients follow you around so you won't have to worry about the work load.
Liability is also a huge issue in my industry. You need to be a registered professional engineer, and being a mining geotech engineer, my cock is on the block everytime I give advice. Insurance premiums are huge. The financial costs of defending yourself in case advice you give causes a mine collapse can be bankruptcy material.
The accounting and book keeping side of it isn't an issue, I know how to do it due to my current job and my fiance is an cpa accountant for one of the world's largest mining companies.
An attractive alternative which I have noticed recently are jobs advertised that are targeting those that are about to set up their own companies. Salaries are in the range of AU$300-350k pa (instead of the average single man consultancy turnover of $450-500k pa), but the workload is guaranteed and you have company backing in case something goes awry.