Probably not calling uart_module_enable

You need bootloader, partition table, and firmware

The ground pad on the module is a single pad but the recommended ground plane on the host pcb is the divided pad with vias. I think this is for thermal considerations and to prevent solder wicking or pooling.

Suggest that you narrow it down to a partition by selectively reflashing the bad image or doing a binary diff to a working image. Also post the log from a cold boot if it is any different.

If you get "waiting for download" you're doing the strapping correctly. Could be a problem with the tx of your usb adapter.

No, but possibly on rev3 chips. There is a new UART_DOWNLOAD_DIS but not sure whether it will ignore IO0 and always boot the application or do something else like halt.

boot:0x3b

For wrover-b it should be booting in 3.3v mode but the strapping pins are showing 1.8v mode, did you set efuse to fix this?

You do really need the external flash because there is no internal flash.

Deep sleep is shutdown/restart but light sleep is suspend/resume.