you may want to consider working with a micropython or espruino or moddable or lua precompiled firmware environment

Yes you have to use pin 9 but most cases you can't use it because it is connected to flash.

Yes you will lose data.

Not bricked if FLASH_CRYPT_CNT can be incremented and/or DISABLE_DL_ENCRYPT=0

Looks like you didn't leave enough space in flash for the bootloader. Bootloader with encryption and secure boot takes up more space.

Either increment the FLASH_CRYPT_CNT efuse to disable encryption or use the encrypt option when flashing

Rmt peripheral has carrier too

If you have multiple app partitions you may not be flashing to the active partition so you could try erasing the otadata. Also you might be using the wrong key to encrypt.

Notice on real devkitc there is clear space around antenna

If you are manually encrypting the bootloader then you have to flash it to 0x1000 and also create the secure boot digest and flash it to 0x0.