If you can benefit from the exemption visa or have a tourist visa, then you can affix your Elite at Suvarnabhumi directly. Currently, due to Covid, I think it is not possible to do it at CM or Phuket
Yes you have to. Elite Visa can be an option to avoid holding 800,000 THB half the year into your bank account to renew your retirement visa. However, I admit the initial cost of it is higher. Just mentioning it, if you want to consider your options
You have the option of Thailand Elite Visa which is for 5, 10 or 20 years. Although the cost would be higher than the classic non-o or non-b visa, it is a fully legal option to stay in Thailand for someone who is not employed and does not qualify to the retirement visa