yes for the process, ask your landlord/hotel to submit a TM30. If staying with your brother, his Thai wife can do, and ask for a print off of the receipt and take along (not always required, but saves a second visit to immigration)
No insurance requirements, beyond what you need to enter the country (this doesn't need to be extended). Booking a flexible ticket could be useful when applying for your covid extension, showing a flight out of the country within the 60 days. (Although not always required)
I used KLM, at the time they were allowing free flight moves. Double check they still do, if going that way. So I just kept moving it inline with the extension I was applying for.
Make a prior appointment online, for your immigration visits
Note, for your 30 day extension, there is no penalty in applying early. You can apply almost straight away, after you arrive, having less than 30 days to go on your arrival until stamp. You will get 30 days added from your existing stamp until date.
HOWEVER for a first applicant to a covid extension, this CHANGE will be taken from the day you apply. So apply near the end of your stamp date and BEFORE May24. The covid scheme will/may (who knows, TiT) close after this date.
as he hasn't had a 30 day extension yet, that's what they would sell him. I doubt he would be offered a covid extension straight off. His only way of really finding out would be to go and ask
same basis as the primary, two independent applications, over 50 or they come here, primary get's a non-o and then the wife goes to wherever to get hers, as trailing spouse