Approval of Design Organisation, as described in Part 21 Subpart J of Annex I to Regulation (EU) 748/2012. This applies for those design activities that fall within the scope of EASA’s work, as set out in Article 2 of Regulation (EU) 2018/1139. In these cases, EASA itself is responsible for managing both the approval process and the subsequent supervision of approved design organisations.

You must apply for an experimental airworthiness certificate (please note that you will not subsequently be able to market the prototype or other identical units without a type-certificate): 

https://sede.seguridadaerea.gob.es/sede-aesa/catalogo-de-procedimientos/certificado-de-aeronavegabilidad-experimental-no-easa

There is no type-certificate validation. To obtain the Spanish type certificate it is necessary to comply with Spanish regulations through a certification process available on the AESA website: https://sede.seguridadaerea.gob.es/sede-aesa/catalogo-de-procedimientos/certificación-de-tipo-ulm

Yes, you can. If not included, the certification process of the model in question should be initiated to include it in the Spanish type-certificate.

All aircraft must comply with the obligations laid down in Law 48/1960 on Air Navigation. Article 151 provides for the following derogation: Aircraft with limited uses, technical characteristics and actions may be exempted, under the conditions laid down by regulation, from the requirements for entry in the Register of Aircraft and obtaining the certificate of airworthiness referred to in Articles 29 and 36 of this Law respectively.

No. In Spain the weight limit for a ULM, in accordance with Article 1 of Royal Decree 2876/1982, is 450 kg. 

Oh, yeah, yeah. The opening of new facilities would be subject to the same approval as the Spanish POA. Only EASA would be required to intervene in this case. It would be a significant change through the addition of a new factory, in which it would be necessary to revisit all the points of the standard, especially those relating to the quality system, as well as to see how this new factory is integrated into the Organisation ' s activity in order to verify its suitability.

Below are two useful links regarding applicable regulations, guides and information needed for POA processes:

Civil aviation production organisations, which intend to produce products, parts and equipment accompanied by the certificate of release to service EASA Form 1. The production of these products, parts and equipment is to be appropriate under approval Part 21 Subpart G, as set out in regulatory point 21.A.133 of Part 21 Subpart G of Annex I to Regulation (EU) 748/2012. Only for direct delivery to final customer (e.g. air operator, maintenance workshop, etc.).

Approval of Production Organisation as described in Part 21 Subpart G of Annex I to Regulation (EU) 748/2012. Applicable for those production activities falling within the scope of work of EASA, as set out in Article 2 of Regulation (EU) 2018/1139.