I obtained a multiple entry non-B in New York in August, and then in December got a new work permit with a new company I set up. I was under the impression that with the work permit, some paperwork could be filed and I wouldn't need to leave the country every 90 days, only check in at immigration. I have just recevied a bill for a new visa (though mine isn't up until August), and it is the big square stamp re-entry one, with "USED" stamped on it, along with an extension of stay stamp. Am I good for another year now, and why would I have needed to get a new stamp? I'm a little confused with this.

Also, I wanted to gain residency after 3 years of paying taxes etc. Is there a minimum salary you have to be on in order to make this happen, and what do I need to make sure is happening now in order to do this in 3 years?

Your visa does not have to be expired to get an extension because the visa is not extended it is your permit to stay that is extended.

If the extension stamp is dated one year from when your most recent permit to stay was for you are good for a year and don't have to leave the country unless you want to. If you do want to leave you will need a re-entry permit to keep your extension valid.

The salary requirement is a minimum of 80K baht to apply for permanent residency.

Your visa does not have to be expired to get an extension because the visa is not extended it is your permit to stay that is extended.

If the extension stamp is dated one year from when your most recent permit to stay was for you are good for a year and don't have to leave the country unless you want to. If you do want to leave you will need a re-entry permit to keep your extension valid.

The salary requirement is a minimum of 80K baht to apply for permanent residency.

How does one get extension of stay when its a new company ? I was always thought you could get an extension until audited books have been submitted for a couple of years

Best to scan the stamps so we can see what you got. (Edit numbers and personal details out)

Your visa does not have to be expired to get an extension because the visa is not extended it is your permit to stay that is extended.

If the extension stamp is dated one year from when your most recent permit to stay was for you are good for a year and don't have to leave the country unless you want to. If you do want to leave you will need a re-entry permit to keep your extension valid.

The salary requirement is a minimum of 80K baht to apply for permanent residency.

How does one get extension of stay when its a new company ? I was always thought you could get an extension until audited books have been submitted for a couple of years

By paying a pile of money to a lawyer or agent.

But unless you go yourself to get it you might have to worry about it being real.