in Prachinburi you have to have 3 months after renewal, (ThaiWife) I know its not correct but its there rule, my point was more about it dropping below the required level where it was ok, seen as a mistake quickly put right.
On my Thaii Wife visa I took some money out of my account holding my 400KTHB seasoning fund, I put it back with 30 mins and it was OK with immigration, so i think it depends on the office
in normal circumstances you should leave the country when your non b becomes void (no work permit) you need to fulfill the requirements fir a new extension based on what you choose, like married to Thai wife or over 50 years (so called retirement), the requirements are on the Thai Immigration website
Depends on where you are, Prachinburi want you to keep the money in the bank for 3 months after the ext is given, they check on the next extension, there probably an exeception.
Last year they did not complete my exit within the 30days and I got a second one, also if you need reentry permit it also takes some space, it sounds like your be ok this year.