Which visa for longer than 90 days in Europe with Spain as primary location? [closed]

Citizen USA, retired. My tentative plans for next year are to go to Spain early in the year and find a low-cost apartment, probably in Navarra or La Rioja. Most of the year will be spent wandering around on hiking trails, improving my Spanish, and acquiring Chinese and/or Dutch online. I will likely volunteer at one or more albergues on Camino de Santiago, though nothing has been scheduled there. One of them has already offered to write a letter for me. Also, part of the year, do Camino Francés by bicycle. And occasional short trips to other parts of Europe.

A website that I read said that if I have official approval for such a stay from a Schengen country, that it would authorize free travel for the duration to any other. However, Both tourist and language course visa says that I would still be subject to the 90/180 rule for all the others.

Different pieces of advice I've been given (opinions of the "advisor," not necessarily mine):

• Retirement visa—easy to get, no conditions on what you do.
• Find a cheap language school as your reason. The school will help with the paperwork. Maybe Spain will do like USA does—if you drop out of school, you're not in violation for a year.
• Don't tell them the entire plan. Just tell them one thing and they won't care what else you do.
• Don't worry about the 90/180 because no one checks except in an airport.
• Don't worry about a visa because Spain never checks (from someone who lived there for several long periods).

Another thing odd is that the government website listed a huge amount of documentation and said everything must be in Spanish. But the application for itself is in English. I'm pretty good at Spanish.

I have to go to U.K. for a couple of days at the beginning, so I will go from there to Spain by bike, bus, and/or ferry. Most likely through France but there are ferries to Spain. Considering a cruise ship or freighter to U.K. (cost comparable to airfare plus meals/lodging for same number of days).

Would want multiple-entry, so I can visit Andorra and Gibraltar. (Possibly U.K. again, and/or Morocco.)

I "hoard" expense receipts, so not afraid of questions on where I have been and when.

So, that's all the gory details, but the question again is (more verbosely), "What is the best type/method of visa application for an American to go to Spain for almost a year and have flexibility for the rest of Europe?"