LTR has to be pre-approved by the BOI in Thailand and can be obtained within Thailand, too. Yearly extensions based on retirement will also be done in Thailand at a local immigration office.
Should be fine. No minimum income is asked. Just the at least 500k THB in savings + a work contract mentioning you are free to work remotely from Thailand / or a company registered in your name.
Good question. Still not fully clear. It seems that some consulates in 3rd / neighboring countries do accept applications from foreigners / non-residents, others don’t. I have yet to see / hear of the first success story of someone successfully having gotten a paper sticker DTV in Laos, Malaysia, Cambodia, or Vietnam. Maybe this question will be answered in a few days when people report their experiences.