How well do you get on with the parents? Negotiate. I was initially told 5 baht gold but then they said nothing because you take care family and love daughter. IMHO if the lady has had children, worked in a bar or been in a relationship before then Sinsod should just be a token amount of gold say 1 or 2 baht. Any cash on display at the wedding should be clearly decided whose it is and what happens with it after the wedding.
Bangkok bank will update the bank book at the counter with a CF line (carried forward) dated on the day you do it. I'd did mine in the morning of presentation to the IO and it was accepted as proof of current balance updated on the day. This was at Surin. May not be acceptable at all IOs
At Buriram Immigration office we went to get Thai passports for family. They wanted proof of vaccination. Just showed them Mor Phrom app vax status. All good.