You need at least 15 days validity left on your "30-days exempt". If you just arrived to Thailand and apply for the "Non-O" during the first 2 weeks, you could probably skip the "30-days extension"...
Yes. Arrived on a "Visa Exempt" in Bangkok, applied for an "30-days extension" in Bangkok, then moved to Jomtien, applied for a "3-months non-O" in Jomtien, and then a "Year Extension based on Retirement" in Jomtien. All went very well. Just have patience. The BKB branch in Jomtien issued the bank letter, no problem. ;-)