Who said you couldn't get it in Taipei? Lots of reports from there saying it's a great option for getting the DTV due to the fast turnaround time and they won't take your money if they won't accept your application.
All land borders with Myanmar are closed to foreigners and have been for years. The only border that's available for a border bounce with Myanmar is Ranong and that's at least a 10 hour drive so.. plus it involves taking a boat to Myanmar.
It's basically impossible to open a bank account on your own nowadays on a tourist entry (which visa exempt is). You would need to pay an agent to help you in opening the bank account.
Why not get the non-O visa from your Thai embassy through the e-visa system before you travel to Thailand? It's all done online now from the comfort of your home and your visa will be e-mailed to you. With that, it should be possible to open a bank account on your own as you'll already be on a non-immigration visa when you arrive in Thailand.
then you cannot apply all at once. You apply and receive your visa first, then you can apply for then others. If you're applying somewhere that requires you to apply in person it may be different, but for e-visa embassies you have to do it in that specific order.
If each person will qualify for the visa on their own then they can all apply together. But if you only want 1 person to qualify for the DTV visa then the others to be dependent upon that visa, you would need to get the first visa separately, then apply for the others. A requirement to apply for a dependent DTV is to upload the already issued DTV for the primary person.
The BOI doesn't contact your employer, but it's very possible they'll want some documents from your employer as part of the process, assuming you are talking about the remote foreign employee LTR. You failed to mention which one so impossible to give an accurate response.
That's all up to the embassy. Each embassy sets their own requirements. So what courses are approved, how long they have to be, etc is all an embassy decision and cannot be answered with just a simple answer that applies to everyone.