You are taking a risk but I would say it is very minimal. I used to do work whilst on holiday all the time before I had a DTV because I couldn’t disconnect from work completely.
To marry a Thai in Thailand you will need to get an Affirmation of Freedom to marry from the embassy, and you need to get it translated and legalised. It was simple enough but I think your starting point is the embassy in Bangkok. I don’t think you can get it in London sadly.