Hi, If you have a job offer from a legitimate Spanish organization or firm that has been properly filed with the ministry of labor, as you know, you can then apply for a visa. Congratulations!! That's the most difficult task.
I believe the medical letter can be done by any legitimate doctor that is obvoiusly registered as an MD and verifiable regardless of the country.
You don’t need proof of health insurance because it’s understood that with the visa you can receive a formal job contract from the same organization that gave you the offer. You and your employer will be paying monthly social security tax which provides you health coverage like anyone else legally working in Spain. It’s also understood that you will be supporting yourself by working for the company that will offer you the contract or they would not have given you the visa.
Don’t forget that once you have your visa and in Spain, you need to apply for a work permit and a residence permit at the same time. This is a breeze because we’re assuming you’ve got a valid working visa. You’ll need to submit copies of your offer, contract, specific forms that certify the Spanish firm is legitimate, copies of your visa, and application to work and reside. This really is a breeze because you can take the paperwork to a “gestoria”, pay them about 90 Euros and they do it all for you. It’s unlikely that you would not be given a work / residence permit because you were given a visa based on a job offer that had been filed with the ministry of labor.
Here is the web site that has all the information you need
www.mir.es Hope I was able to give you information that you didn’t already know.