Can I apply for a retirement visa while in Thailand on a tourist visa, and when can I obtain a tax number?

As you have a bank account these are the general steps you need to take.

1. Get yourself an address and then go to immigration and complete the TM30 process. Your landlord may do this for you but you will need to go for step 2.

2. Ask immigration exactly what you need to do to a Non Immigrant O. Also ask what they need for the 1 year extension.

3. Depending on the area where you are living will determine whether you need 800k seasoned in a bank account for a period of time. The 800k will need to be sent from outside of Thailand.

2A if your money needs to be seasoned for 2 months you will need to apply for a 30 day extension on your visa exemption or tourist visa.

3. Apply for a Non Immigrant O based on being over 50. This can normally be done when you have 30 days remaining on your current stamp. In certain immigration offices this can be done 45 days early.

4. When you have days remaining on you Non Immigrant O stamp apply for a 1 year extension. Again ask at your immigration office for their requirements.

Keep in mind re-entry permits. Basically the rule is whenever you leave Thailand you need a re-entry permit.

That’s how

Most people do it. But use an agency.

You don't actually need an agent but some folk might like to spend the money. You've got a bank account so the rest should be easy enough.

The answer is yes.

But you might want to consider using a visa agent to facilitate all the necessary steps, including opening a bank account

Actually, you came as a tourist, flying to a neighboring country and returning on an O-visa.

You can enter on a tourist visa but if you don't already have a Thai bank account you will find it almost impossible to open one and unless you come from a country where you're embassy issues an income certificate you won't be able to apply for a retirement visa, so you would need to leave Thailand again to apply. The tax number will be between you and the revenue department but you don't become a Thai tax resident until you have spent 180 days or more inside Thailand in a calendar year

Yes. Just find a good agent.