There are only formalities for Non-EU nationals importing household posession from Non-EU countries.
When a Non-EU National takes up residence in Spain they may import their household possessions free of customs duty.
This is a once only concession. It is not dependent on the purchase of property.
It is necessary to make a deposit of about 50% of the value of the goods which can be reclaimed within a year on production of a residence permit or card. The form can be obtained from a Spanish consulate.
There is a lot to go wrong so use a professional removal company. Make sure the contract is to deliver the goods to your address in Spain and be alert to reclaim the deposit within one year or it will be forfeited.