[kops]

No idea about Portugal, but in some countries you don't need to register a company or any other legal stuff unless you do more business than a certain threshold. Find out in your country what this amount is. Later on, if you cross this threshold then hire an accountant to setup the business as a proper legal entity. If you make enough money you can hire an army of people to help you out. If you don't and assuming the service is cheap, and if a customer goes nuts then just refund. Set aside a small amount as the risk you are willing to take and do not cross it i.e. do not sell more than this amount. Check out how you will accept the money, and if your payment processor imposes any restrictions w.r.t. legal status of the business. Good luck and congratulations for making something that you are confident that people will pay for.