Total available RAM size on ESP32 and the meaning of `ESP_STACK_SIZE`?

Try to answer question 2:
Just realized 2300 is actually the number of JsVars allocated for Espruino. The number is automatically calculated in targets/esp32/main.c based on the available heap - 40000 bytes (I guess it's for the Bluetooth stack?).
So the approaches to increase the number of JsVars (e.g. RAM for Espruino) could be:

• remove unused libraries from build to save more heap space (remove that 40000 if Bluetooth stack is removed)
  
• decrease the ESP_STACK_SIZE to allocate less DRAM heap for Espruino task's stack