Can I apply for a 90-day Non-Immigrant O visa (retirement) in Bangkok without leaving Thailand?

Hi people, need advice or confirmation of my understandind about getting a non imm O (retired 90 days). I'm canadian, living in Samui since july 2016. Got a one year non imm O retired visa in Canada and got one year extension here in Samui last July 2017. Went to Myanmar last february for 3 days and was not aware that i neded to get a re-entry permit as my original visa was a multiple entry. Anyway got a 30 days stamp at airport (Don Meang) and a 30 days extension here in Samui. Questions: 1- I believe i can get a 90 days non imm O visa (retirement) in Bangkok? To avoid travelling outsie Thailand!! 2- Where would be the ideal immigration office, division 1 since i see 5 locations on web site. 3- Need to fill out a TM-87 visa request form? I can download! 4- I have affidavit from my embassy to confirm income, 2 pics and passport, do i need anything else? 5- And i can get one year extension anywhere (Samui) or best to do in BKK? 6- Finally, DO I GET THE VISA ON THE DAY I GO ATT IMM OFFICE? As i planned to be in BKK on the 02 April (stamp extension til 18th april) and return to Samui 7th April. Thank you very much to share advice and taking time to read this as i not expected to have to worry about my visa upon returning from Myanmar.