You need to have a NIF number (probably a Model No. too) to be able to operate as a self employed worker. Initially I was set up to work under 'regime simplificado' as a self employed person but that regime stopped a few years ago and I had to be set up differently. The rules may vary for those who work from home to those who are based and run an office and have other people working with them or for them. You should seek professional advice about what it is you are required to obtain based on what you want to set yourself up as, as rules change annually. Over the years changes included paying 20% tax down to 4% tax and now no tax if you earn under 10.000 Euros a year.
Some people have been told they don't need to record expenditure or keep receipts under the 4% ruling, while others say yes they should have done this. Apparently as from January 2017, I now need to record my income and expenditure in two different official books as well as use an official Factura Invoice/Receipt book........... but there are different requirements depending on what it is you do and how you operate. Please go check it out yourself. I could be given more or conflicting info the next time I enquire!
You will be required to produce some documents to Finanza to be able to set yourself up to work in whatever capacity in Cape Verde.
Look into what visa you require to be able to work.
This is the website through which you register to be able to pay certain taxes. There is some information for business, residents and non-residents on the Porton website. For more info visit : www.portondinosilhas.gov.cv