Hi, I'd also start with a very simple business plan - one page would do it - of your business mission, goals and objectives, your target market, products and services, how you will finance the business and a very simple marketing strategy etc. A google search will show any number of templates you can use.
What is your set up budget? What products and equipment do you need? What room are you using? Is the room ready? Are you going to have a website? Prices? Check it's ok with you local council? Insurance? How you going to get clients in? Tax man needs a phone call? How u going to book client, will you have a gap in between clients do no one is waiting. It's worth doing a search because there is loads of helpful info on this good luck