Being a remote worker is not enough. You need to work remotely FROM Thailand and your employer needs to give you permission to do that along with a statement that you won't work for or interact with clients inside Thailand
probably best to think of it as the extension just carries on until it's permitted date whether you are in Thailand or not, assuming you get a re-entry permit
yep you can do that, either a single re-entry permit or a multiple but be aware it doesn't add any time, just keeps your entry stamp alive when you leave
you don't need a criminal police check for an extension of stay. Depending which visa you apply for you may need one but that's most likely in your home country before you travel to Thailand
Given you say you have paid for a multiple re-entry permit I doubt very much you are on any visa. It's much more likely you are on an extension of stay based on retirement
You need a reason to apply for the DTV visa, either you are a digital nomad (working remotely from Thailand) or you have to sign up for a minimum of 6 months soft power activity. Its not really designed for someone just to come and truck about
When you enter Thailand you will get stamped in for 90 days. You will need to open a bank account within the first couple of weeks as to apply for a 12 month extension of stay (not a visa) the money must be in the bank for 2 full calendar months. To open the bank account you will most likely need a residence certificate from your local immigration office. And yes you will need a Thai mobile number in your name. Retirement extensions are normally issued on the day but if you want to leave after that you will need a re-entry permit to keep it alive, you can get one either from your immigration office or at the airport. You need to have a minimum of 800k baht in a Thai bank for 2 full calendar months before applying for an extension. Getting a Thai licence is pretty straightforward if you have a home license and IDP, you go, you apply, you do a couple of very basic tests and they give you a 2 year licence, when you go for the next one they will give you one for 5 years