Take both passports with you. On entry they’ll stamp you in for whatever visa you had in your old passport. At your leisure visit immigration to get any stamps transferred
Depends where you are in Thailand. To get a new passport you can use the company VFS to apply. Or use a service like Mike’s Sending Machine.
Once you have your new passport it’s relatively easy to get stamps transferred. It doesn’t cost but you may have to make copies of every used page of your old passport and the data page of your new passport.
If you get a new passport in the UK then you’d need to enter using both passports and then go to immigration to get your visa/extension stamp transferred
We will have to wait and see. No one is going to be trying to get one for 5 months or so. If the regional head of Division 6 and my boss at immigration say it’s going to be 10k then I have no reason to doubt them.
The MFA and Immigration are two entirely different government departments. Immigration set the rules on what happens with visas and extensions in the country.
Different immigration offices often have different requirements for extensions and the like but there is no way that one division will be charging 10k and another 1,900 baht.