Earlier quoted context omitted.
Any suggestions? Spain has been a potential target for temporary relocation for me!
I got the impression that English level is really poor in Spain (when I was visiting Valencia, didn't go to Barcelona). Even with younger population - I was going out in the evening with some friends, we approached like 4 groups of 20-something and none of them could even give us basic directions. In shops and tourist places it's better but barely.
And although I wouldn't worry too much about language too much if your focus is primarily on work, Spanish is perhaps the easiest language to learn as an English speaker. You can achieve professional level fluency in 600 hours of study. Certainly with 80-100 hours of concentrated study and continued practice after that you can learn more than enough to get by in daily life.
Two big advantages with learning Spanish: 1) pronunciation is easy to learn and is the same for both written and spoken Spanish; 2) there are lots of cognates, so if your English vocabulary is good then you already know lots of Spanish words.
Spain is great, but for the purposes of picking a country for working remotely and having a longer runway, I would argue heavily for Mexico over Spain if you're picking a Spanish speaking country. The overall cost of living is low, internet access can be great depending on the area, you'll be on a similar timezone as the US, and services (cooking, laundry, babysitting, etc) are very inexpensive - leaving you with much more time to work (or to use your downtime more effectively than running errands/etc).