All savings accounts with the exception of one special one at Krungsri pay 0.5%. The special one at Krungsri pays 1.3%. But is heavily restrictive. You have to maintain a balance daily over 100k thai baht and can't use the account more than 3 times in a month. SCB pays the best rates on fixed term accounts or the equivalent of a CD in America.

ANY work conducted in Thailand weather its a real job or volunteering requires a work permit. They have specific ones for volunteers

Depends. If the condo is valued over 10 million baht you can get an investment visa.

Yes and yes

Mine is 100% legal

Its my second one. So I'm guessing till i run out my time on it

Haha. I would not post that on social media. But I can be done. I am walking proof. I got a 1yr non-b on my own in my home country

No. You can get on your own. But its very hard.

If he no longer has the job it should have been cancelled. How ever you do not need a work permit with a multi non-b.

This is correct. You don't need to leave every 90 days. You can do the reporting online or at your local immigration office.