Hello. Ok, I have a complicated question about My ED Visa when it comes to traveling.

I am going back to Australia in May, then planning to go to Myanmar with my girlfriend. At first, I thought I would just meet her in Myanmar, but the ticket prices from Perth > (connecting in SG or Malaysia) to Myanmar is more expensive if I were to go to Perth > (connecting Malaysia) > Bangkok > Myanmar. Also the transit times are the same roughly just more planes.

I know I have to go to immigration to notify and pay when I leave Chiang Mai Thailand, but there may be a 4-5 hour period when I'm in Bangkok before going to Myanmar which is not a connecting flight, can i go into BKK and visit friends then go back to the airport without doing anything with my ED Visa?? What is the procedure here? Thank you in advance!

I'm on an O visa, I'm going to Myanmar on the 17th for a week, should I go to immigration and get a multiple entry stamp before I leave the country if I don't what will happen?