I have not done the process myself, so excuse if I do not have all the facts.
I do know several practitioners (my chiro, osteo and dentist all run their practices from ‘apartments’)...
who have a business in a primarily dwelling situtation.
I am thinking if it is a community building you will have to get the permission of the committee (which in theory could be all the residents in the block as they should be attending these meetings for their own benefit!)...
Some will be Ok with it, others not!!! (Case in point my Osteo who has had his practice running for 6 years no problems, then due to strained relations with one of the other apartment owners, she keeps ripping his name tag off his front door bell???)..!!!
As for legalities… you need to get the right legal advisor (please be careful and only pay when you are satisfied with their services as there are many poor ‘advisors’ out there and they will happily take your money and do very little/the wrong thing!)
I am guessing you will need a ‘licence’ of some kind to operate as well as insurance, SPANISH qualifications, health and safety, tax registration, social security registration etc, etc.
Please research your legal advisor as much as you do setting up other parts of your business! (It could save you alot of trouble down the line.) I am guessing that when you have made a success of it from your home and are ready to open up in a dedicated space outside of there, you will have to jump through a whole new set of hoops. But good luck! (There are those who have done it - look up La Chispa magazine, they are perhaps a good starting place.)