@bluewavenet thanks, I flashed the ar71xx version and it works (though the eth0/1 swap is annoying if you are restoring a backup).
Re: the power supply, the AR300M was using a 2A power supply, and I don't have anything larger for < USB-C. It is the same brand and style as the one I was using for the AR150, so I swapped it with another 2A supply I was using on a Raspberry Pi that I believe is good.
Re: NAND, I've probably had enough adventure for this week but is the procedure you're envisioning different that what's at GL-AR300M and GL-AR750S NAND Support (ath79) ? Because I think I did it correctly: flash NOR, boot that, use that to flash NAND, reboot, and bricked. I did it twice, using uboot to recover both times.