Thai embassies are outside of Thailand so you need to be outside of Thailand and enter Thailand when you have the Visa

Why is this question posted again and again , if your not a resident or citizen then you need to follow the visa policy

Firstly are you getting a Thai mortgage ?

As the house will be in your wife's name 51% then the mortgage will be paid through her bank account normally , we'll that's my experience .

Try Kasinkorn Kbank and go with your wife , I tried Bangkok and few others and they always want a long term visa .

The marriage visa seems the best path for getting more from Thailand but the 400,000 baht or £10,000 is a lot of change . You can withdraw after but needs to stay in the bank for over 2 months .

You can get your marriage registered at the local Ampor office/municipal area office . Take your UK marriage certificate plus your wife will have to show the name change possibly too .

Plus might need other documents.