Self-Employment or Company?

Depending on what type of business you are thinking of setting up I'd ask the advise of a commercialista as there are varying forms :

s.s simple society usually a single or couple self employed with IVA number to reclaim vat, S.A.S = LTD company, SRL = very large company with many employees. If you don't think turn over will be massive don't bother with the IVA number as the tax office is a pain to deal with and the accountant will cost a  minimum of 1k per  year, also the tax office assume a minimum amount of turn over/profit to particular types of business and its down to you and the paperwork to prove otherwise so an accountant is essential and the cost is better than trying to fathom the tangled legislation by yourself. A cheaper way is that some societies will do you tax papers for a minimal sum but generally its farmers, farmhands who use these services and there is an annual fee to join but cheaper than a registered commercialista.

.Try asking Gareth Horsfall Spectrum IFA on face book he's very approachable and knowledgeable if he can advise he will.

Good luck