Having been there and done it twice.
Cover your legal obligation.
Calculate the cost of being open.
( I had to sell £1400 worth of tools per week just to cover the over heads, bank, van etc and take £100 wage, that was in 1989)
Then consider can I ever earn big bucks by it?
A lot of self employed people often are earning less than minimum wage as they often forget all the hours they spend doing paper work, updating web site buying stock etc.
Be realistic start small, decide how much you are going to invest if it dosnt go to plan walk awayas people often throw money at a problem and loose it.
Why not keep your existing job and deliver vehicles at evenings weekends etc?
Brake cars and flog bits on internet in your spare time?
If you then see a good business give up the day job.