If you decide to transfer your tax residence to italy in addition to your professional activity.You will have to apply for the following (regardless of whether you are an eu citizen or not):

An italian tax code.
A vat number for self-employed.
Your tax code, which is equivalent to the spanish nif (fiscal identification number), is a 16-character alphanumeric code.
You will need this code for the following:

Register with the national health service

Open a business in your name.
Enter into a contract (eg, rent , sale, etc.).
Hire a bank account.
To request your tax code, you only have to go to a consulate or an office of the tax agency. You will have to present a valid id or your passport. As we said before, you will be assigned a tax code automatically if .You come from outside the eu and have applied for permanent residence in italy. If, for whatever reason, you do not have a tax code and you come from outside the eu. You can request it by presenting your residence Phone Number List permit at an office of the tax agency.

Your vat number is an identification code that every person or company that. Has economic activity must have in order to open a business in italy. You will have to go to a tax agency office with your dni and the aa9/8 form for individuals.(sole proprietorships and self-employed workers) to obtain your vat number for self-employed workers. You can also request it through the post office, the tax agency .Website or by contacting an intermediary, for example, a tax advisor or a tax assistance center (caf) in your area. If you wish to obtain more information, consult the section that the website of the tax agency dedicates to this subject.

The reason and length of stay are always indicated on the permit. Apart from allowing you to work as a freelancer, this document also helps you:

Enjoy all the rights and services obtained by foreigners residing in italy

Register in the civil registry and obtain a dni and a tax code. Which will allow you to request health services, open a bank account, etc.
While you wait for your residence permit to be Sale Lead issued. You can legally reside in italy and, if your entry visa allows it. Continue to work. A residence permit for self-employed workers is valid for a maximum of two years.