dont book the flight but get the flight number for your intended travel date from the airline site and use it, that will be ok....

if its Japanese passport then yeah as the place of issue Japan, i have USA got in Canada since i am dual but i always use USA as place of issue for USA passport

Vietnam is the worst when it comes to board out of there country.....

you dont need to buy ticket, just pick a date and find flights online and write down the flight number.......same for hotel or accommodation

i got mine before i even applied :)

i would say go for EUR to be safe

Once you get the DTV you will NOT have any issue to enter Thailand. you can even apply tourist Visa from embassy and go to Thailand without any issue (i have done it before i got the DTV), they only banned you for using visa exemption too many time in one year (dont argue with me about there is no mentioned the limit anywhere, i am just telling you what i have been told by the Thai IMMIG), i am sure if you wait another 6-8 months outside Thailand then you can even come with visa exemption....

you can do anything for anyone OUTSIDE the Thailand..

lesson learned so all good.....glade to see your positive thinking....

i myself also thinking to get Indonesia’s digital nomad visa, always have a backup plan and no harm to have another visa if you can......good idea in my opinion