You don’t have to travel to Portugal in order to get a Portuguese tax number. Furthermore, You can start a business in Portugal as a Golden Visa holder.
Getting a Portuguese tax number is a very easy and free process. This process can either be done by yourself or by means of a Power of Attorney granted to someone who will become your tax representative in Portugal, as you are not a regular resident. The needed documents are your passport or certified copy of it, if the application is performed by means of Power of Attorney; a proof of address of your current residence issued within the 3 months prior to your application. Once gathered, these documents must be submitted at a local Tax Authorities Office (Autoridade Tributária e Aduaneira), which will issue your NIF on the spot.
That is correct. Before you invest in real estate in Portugal, you will need to have a Portuguese taxpayer number. You can obtain a taxpayer number (NIF) through a Power of Attorney given to your tax representative in Portugal (a person or entity that will represent you before the Tax Authority in Portugal).