What do I need for my first 90-day report in Thailand after getting a DTV?

Extending the stay and the 90-day report are totally different things, not really related to each other.

90 day reports and extensions are not the same thing. For a 90 day report you just need a TM30 receipt, a completed TM47 form and your passport

Are you extending or 90 day reporting ?. You mention both

If it were me, I would come prepared with all of that info.

Are you still doing the course of stopped, what are you going to do in Thailand for the remaining 57 months, of course you are free to leave and come back in a few years but your DTV clock started on approval. When you return you might get pulled up or go straight through, just be prepared to answer any questions they may ask and provide the paperwork

No one can tell you what will happen. Probably better to go for a short trip to a neighboring City and fly into Don Meaung so at least you do t come across as a cheap Charlie going for a border crossing GL keep us posted on the outcome

From my understanding, you only have to write down where you’re staying.