International Drivers license for Spain

Yes, it is necessary to have an ID Permit in Spain. While necessary, I’ve never been asked for it, but I’ve never been stopped. I’ve read of steep fines if stopped and you don’t have it.

Yes, it is, not necessarily for renting but for driving.

It may not be necessary to "rent" but you better have it if the police asks to see your DL.

Yes. You will probably not be asked to show it when renting the car, which leads some people to think it's not necessary. However, if you are in an accident (your fault or not), or stopped by the police you would need to show it. I would not want to be caught by the police in another country without the required permits! It's something like $20 at AAA and all you need is a current US license and a passport style photo (they will take the photo if you need it). It's basically just a form translating your license and providing info.

Yes! If you get stopped and don’t have one-big fine!

https://es.usembassy.gov/u-s-citizen-services/local-resources-of-u-s-citizens/information-for-travelers/traveling-to-spain/

Yes, IDP is required to legally drive in Spain.

And it is an International Drivers Permit, not license. It must be presented together with your valid license from home when asked for.