Two jobs in Spain? Is this possible

I am working in Spain for over 2 years now, paying my taxes and social security. Now I would like to open a company here in order to make the invoices for the addicional jobs I am doing sometimes, and the questions pops to my mind.

How is it if I want to be a freelance and keep my existing job in the same time?
Is this possible?
If so, will I have to pay Social security twice (my company I am working in is paying one for me)?
What about the tax level?

Any comments will be highly apriciated.

Kind regards,

Jackie

Generally speaking, if you are self employed and pay your own social security etc. you do not have a job. You can invoice anyone for work done for your clients. If you are employed, you have a labor contract, and your ss is paid out on top of your nomina. If you are employed full time (40 h per week) you are unable to legally work anywhere else, if you are part time, you can. If you earn more than 70.000 per year it becomes interesting to form a SL company. The tax levels on self employed base income is the same, no matter if you invoice one or more different clients.