1. My wife has a health insurance in Thailand, they also issue the required Covid certificate. Several insurers offer Covid only insurance in Thailand, and for sandbox, she needs one.
2. No sandbox hotel is allowed to include covid tests, you need to book them separately as per guide line before obtaining the final CoE. Find the test location close to your hotel when booking, so it's easy to get there. Initially it was intended that the hotels can handle the tests, but this did not work. Anyone offering the tests did not adjust their website and might or might not deduct the price for it (8000 Baht pp) when booking.
Obviously, ASQ quarantine hotels do include the tests, as you're not allowed to leave your room for 14 or 15 days.
3. My wife and I got the CoE issued within 3 days, other embassies might take a little longer. Certainly, sandbox is a million times better than quarantine, but slightly more expensive over all unless you only eat Thai Street food for 14 days.
4. Flights most likely will run, but can't say for sure until the day you require it. We will be hiring a private car which will take a few hours but not much longer door to door and will not require any additional Covid tests.
There are a few steps involved, but if you follow the guide published on the Thai embassy website it is quite straight forward. You must apply for CoE in the country you start your trip from irrespective of your nationality and should have stayed in that country for 21 days before departure.