Apply for a single entry non immigrant B visa. When you arrive and have your work permit then your single entry non immigrant B visa will be extended for the duration of your work contract. There is no need to get a multiple entry visa as teachers are exempt from doing the 90 day border bounces. If you want to leave Thailand to go overseas you can get a re-entry permit. You can obtain a single re-entry or multiple re-entry permit from your local immigration in Thailand once you have arrived. With regards to the leaving date on your arrival card, simply state 90 days from your original entry into Thailand.
I did the same. I have been here for 8 years without having to do any border bounces and l came in on a single entry non immigrant B visa.
In certain jobs in Thailand you need to have a criminal background check. It was law for teachers to obtain said check after 3 of the top 10 most wanted list by Interpol were found to be working in Thailand with work permits as English teachers a number of years ago.