Skipy
Having been self employed for many years until health issues upset the apple cart, I would add the following.

Make sure you have a lump sum of money set on one side for the first 6 months to make sure you can pay the bills in case things are slow.

Make sure you are covered for public liability insurance.

If you can use spreadsheets, it is very easy to keep daybooks for all your sales invoices, purchase invoices, profit and loss account and balnce sheet etc. If you need any templates, then Pm me with your e-mail address. I still do the books for my wife and file my wifes self employment returns online. I don't use accountants as i already have that background. Keep every invoice filed with the spreadsheet printouts so it is easy to check everything. Obviously if you do not have an accounting background, tidy daybooks with all the invoices makes it a lot easier for an accountant to do the results for you and will save you a lot of expense.

Get private medical insurance, so that if you need to go into hospital, you can do that at a time that suits you and your work.

Cheers
Les