Assuming you are going for more than 45 days, do yourself a favour and get a 60 day TV. It will negate any potential problems with the airline on way out. Also, it’s just wasted time and hassle at immigration office when extending your stay. The cost of the TV and extension are comparable, so no real advantage in not getting a TV.
Because you’ve read it wrong. He’s currently on his extension now, but thinking about what happens in 3 weeks time when it ends and he still has 6 days left in Thailand.
A bit of forward planning on your ED visa could have sorted this for you. You could have opened a bank account and transferred a monthly 65k baht for 12 months while studying. Then, when it came to applying for your retirement visa, you would have had proof of funds without having to go down the 800k route. Not much use now unless you can continue on an ED visa a while longer and happy to be corrected.