Hi, I hope to answer your questions.
My understanding is that foreigners are required to have either business visa or work permit in order to conduct business or working in Myanmar, not stay permit. The stay permit is required when the person holding the business visa extends their stay.
I have entercountered some local companies offer a job but without the arrangement of work permit or business visa. You may have to arrange it yourself. Depends on your resident country, you may be able to apply business visa via online. If is work permit, you may have to go personally to Myanmar embassy in your country.
My understanding is that the business visa will allow one to stay for 70 days in Myanmar. Thereafter before the expiry of the visa, you can apply the extension.
The duration for business visa application is about 1-2 days or 0-1 day via online. I have no idea about work permit but it surely requires more documents and time than the business visa.
