Employment status

Good morning, I am an employee and I am thinking of providing my services as a Fire Risk Assessor on my own, what is the best approach? Becoming a self employee, soler trader,...? How that would affect the salary I am currently receiving from my company? My small business potentially may not invoice anything, especially at the very beginning, what are the obligations then? Do I need to pay any kind of fee or monthly fee or similar? Thanks Kind regards

Hi,
Please see the following information:
Set up a business
Employment status
Thank you.