LINK to Tourism Law Autonomous Region of Murcia.
Rural properties that are offered to holiday makers are divided in two categories: Casas Rurales and Hospederías Rurales.
You will need to register your property by filing a ´declaración responsable´ and apply for a classification of your property. Look under ´documentación´ for additional documents to present. Licence of First Occupation (LFO) is one of them.
More info HERE. You need to print the declaration, fill it out and present it in person at one of the offices with access to the Registro de Empresas y Actividades Turisticas. At the end of the webpage linked to above, under ´Donde y cómo tramitar´ you´ll find a link to the pdf form and below that, under ´lugares presentación´ a link with listing of offices.
Another category of properties is ´Viviendas Vacacionales´. Info on how to register HERE. Look under ´documentación´ for additional documents to present.
Apartamentos Turisticos is a third category. Info on how to register HERE.
A ´responsibilidad civil´ insurance is obligatory for all tourism activities in the Murcia Region.
I have not been able to locate a specific list of requirements for each category of tourist lodgings, like there is for Andalucia for example, so I strongly advise to visit one of the regional offices mentioned above to ask them for advice on how your category would be classified, and enquire about any additional paperwork you would need to submit, and any obligatory features in/on the property with regards to temperature control, safety, disability access etc.
Also, all those involved in holiday letting are called ´empresas´ in the Murcia Tourism law and that makes it a bit hard to distinguish in what cases you would be required to register as Autonomo/self employed (issue invoices with IVA, file IVA tax returns etc.) and in what cases you would be only be required to include the rental income in your RENTA declaration (if resident) or quarterly filing of Modelo 210 (if non-resident). So I would highly recommend visiting a gestor with experience in this matter as well, before engaging in any of the activities that are covered by Murcia Tourist Law. And visit your Town Hall to enquire about the necessity of an opening licence.