Costs of self-employment in Spain

Hey,

I'm self-employed back home (Poland, EU), I am a tour leader. I usually work as a tour leader employed as a self-employed freelancer by Polish travel agencies, who send me to Spain. I would like to move to Spain, and I'm considering closing my company in Poland and opening it in Spain. I sincerely hope this would allow me to live in Spain, which is my main goal.

My question is: what are the costs of self-employment in Spain? In Poland, we pay the equivalent of about 200 ? per month (health service, insurance etc), plus 18% of income tax. What does it look like in Spain?

Is it possible to live in Spain but have a company registered in another country? Is it possible to issue Polish invoices in case of a self-employed worker employed by Spanish travel agencies (or companies in general)?

Agnieszka