As others have said, right now it doesn't particularly matter. Immigration at the border do not look at this. If you never need anything from immigration in country you may be able to just never do them at all. Personally, I am going to do them regardless, as it is still a legal requirement and there are other things that used not matter, but then started to matter. (Like overstays- you used be able to just pay the fine and as long as you paid this it didn't matter if you were overstayed for years. Now that matters a lot, and overstay history can matter if applying for a new visa.)
immigration will almost certainly want to see the passport with the entry stamp. Check in are unlikely to care about that. If you have both you'll be covered either way.
it could work either way. Elite used work this way, and you could get an extra year by stamping in right at the end, but they changed it a few years ago and if you re-enter in the last year they now only stamp up to the end of the visa.
The legislation introducing DTV isn't clear on what happens with entries but it does explicitly say extensions cannot go past the validity of the visa.
If I were to guess, I suspect they will only stamp up the end date of the visa. But as Adam says we'll have to wait and see what happens.
it was 43 a month ago. If you wait it could go back to that. It could also get worse. No way to know, if anyone did know they could make a lot of money on it.
you're doing something wrong, as it won't cost £19,758. The exact amount changes constantly with the exchange rate, but it's almost £1,000 lower than the number you are saying, I checked and it's giving me £18,848. The Where are you getting the idea it's going to cost £19,758? I think you must have meant £18xxx, no? The £120 fee is reasonable, the exchange rate is the midmarket rate which you can't get better than. What comparison list are you looking at that suggests you can get better?
Anonymous participant with 90 day "first time" is relative to your current entry, not the visa. If you are on a DTV, leaving under 180 days, it's always your first time. If you did it early on your current entry and you need to do a second before the 180 day, or if you extended, yes you can use the online system for a second 90 day report on your current entry stamp.
yes that's what it says. Could save an hour's trip though. I haven't done it myself but I may try to see if it works. As I was set up on the system I did try doing my first one online after an entry (not first on the visa) before and they rejected it so I know that's out.
it's very low. Well under 1%. For USD to send 65,000 THB Wise charge 0.68%, or $13.79. That's $165/year, or 5,300 THB. I think you need to see that as a "cost of doing business".