If your flights are all booked on one itinerary and you get all of your boarding passes at your departure airport, you won't have any issues. I've transited Doha 4 times during covid and never been asked for anything.
Just 90 days at a time according to the person I spoke to. Before applying for the extension you need to have the next 90 days booked. Definitely no need to book all 9 months upfront.
I spoke to someone at the Thai Embassy in DC and they said Airbnb will work to satisfy the accommodation requirements and to simply upload booking confirmation showing the address, confirmation number etc. I've not finished my application yet so can't say for sure if that actually works, but this is what I was told.
yeah I'm not thrilled about all the restrictions attached to the STV. I don't know that I'll qualify for any other type of visa at the end of my visa exemption though. I guess the exemption still seems pretty appealing since I'll have 4 months basically free of restrictions even if I can't get some other type of visa at the end.