Your flight to Saigon is the perfect proof of onward travel, as the airline flying you to Thailand will want to see a proof that you leave Thailand within the 30 days stay permit, you will get stamped in upon arrival
Immigration generally rarely asks for proof of onward travel. This question is reserved for offenders of multiple consecutive visa-exempt entries.
For the flight back to Thailand, your return ticket to the U.S.A. is, again, the perfect proof of onward travel within the next 30 days stay permit.
Keep in mind, PRINT all the tickets on paper. Most check-in staff will thank you!
this is not true! Only foreigners married to a Thai wife will have to get their marriage registered at the Amphur. A married foreign couple can use the embassy and MfA certified documents as proof of their marriage being real, for immigration office purpose. They do NOT need a certification or a Kor Ror 22 by the Amphur. What you talk about is already certified the very moment the MfA certifies their marriage documents
even if he was an European citizen,your reply would be wrong. He will get a visa-on-arrival for 45 (!!) days in Vietnam with a Schengen passport. The days of the 14-days VOA are long gone for European citizens. But NOT for U.S. citizens
their French marriage documents are already certified for use to apply for a Thai visa in France. Only to be able to use them inside Thailand, they need translation & legalization by the French Embassy Bangkok, and further probably immigration will require the legalized documents "cross-legalized" again, by the Thai MfA in Bangkok
"Did you need to find a sworn translator in order for the translation to be admitted by embassy?" . . . . you need a French Embassy Bangkok approved translation service. I reckon you will find adresses and link to these translation service on the website of the French Embassy Bangkok . for a start, try here
the fee to apply for the "change of visa type" would be 2000.- THB, and the fee for the application to the 1-year extension of stay will be 1900.- THB. But you should first READ about the rest of the requirements you need to fulfill for the application to the change! It's NOT as easy as applying for the 90-days Non-Imm-O visa on the Thai Embassy in France and entering Thailand on that visa. READ HERE: