Can I apply for a multi-entry tourist visa to stay in Thailand for 8-9 months per year?

Last month after maxing out my METV I returned through the DMK airport in Bangkok after a 5 week absence. I wasn't that concerned about coming in visa exempt since I had a valid reason with a clearfile full of documents to show them why I was coming back in. I was pulled aside as expected and was told that they couldn't let me in as "a regular tourist" as I had spent longer than 180 days in country in the past 12 months. I had to talk to their superior to be let in. But based on that 180 day calculation I would suggest you time your back to back visas so that when you re-enter that you have had enough time away to not trigger that number. ie do your 8.5 months in Thailand, go elsewhere/home for 6 months. On another note, I was also talking to my Thai friend who works in investment and tax accounting firm last week. He told me with the new tax laws they are advising their clients to keep under 180 days in a tax year to avoid paying the new Thai tax if it gets finalized.

Try until they stop you.

it is almost impossible now to get a "trailing spouse visa" from embassies or Immigration for your wife. Only some embassies seem willing to hand out a "trailing spouse" Non-Imm-O visa, if the main applicant holds a Non-Imm-O/A visa. You could email your Thai embassy or consulate and ask them if the accept a "trailing spouse" visa for your wife for the next three years, until she can apply for her own "retirement visa"

Thai immigration is not that stupid. They will soon see you're trying to live in the country by by-passing the long-term visas. Perhaps you'd be better off looking at a visa which suits your plans

I think it would by quite hard to get a second METV so short time after you’ve maximised the first one in the first place, and you might need to look into other options. People who don’t qualify for long term visa often apply for a ED visa’s for to be able to spend more time in Thailand and learning thai. The school has to be approved by the thai immigration and they’re cracking down on people who’s enlisted and don’t attend classes.

Very possible but you will be a tax resident and have to fill in a Thai tax return if current rules are followed through

Retirement visa

Do it until you cant.

I'd say you might get away with it for 2 years, but even that I'm not sure about.

You CANNOT live in Thailand without a long-term visa, and 8-9 months is living in Thailand. Eventually either the embassy will stop selling it to you, or immigration will tell you that enough is enough.