Yes mate - need marriage certificate then usually things like wife’s tambian baan, copy of her ID card, your passport and all stamps in and out of Thailand. From my old experience your options are : multi entry non o (I think) - basically means you are good for a year but have to leave every three months BUT no money in bank needed - or entering on a single 3 month marriage visa which you can then extend in Thailand on the basis of showing the 400k. For both you need marriage certificate unfortunately... so you would need to re-enter on a different visa then marriage if you can’t sort the certificate before you go to Nepal. Bit of a headache of paperwork but it can be done !
Yes I first applied online with the e visa service. And at the end of the process, you are given the option to hand it in in person - or to post it in. You must send the full documents, passport picture and 10 pounds in cash for return postage. And send it to them by "Royal Mail special delivery" service. Fingers crossed - my passport arrived with them today :)