NodeMCU Firmware

Get the firmware

Get the NodeMCU firmware here: https://nodemcu-build.com/
You might wanna include at least these modules: UART, WiFi, net, file, SJSON, timer.
SJSON will not be a requirement, though.

Uplaod the firmware

There are countless ways to uplaod the firmware. You might wanna try one of the simple GUI based tools. If you're crazy you can set up a Linux machine (or use an existing one) and install the countless requirements (you might wanna use this as a reference then.
Or you can utilize Docker to take care of the flashing, which is what I do: https://github.com/T-vK/docker-esp-sdk

If you have installed docker and pulled the docker-esp-sdk image, you can flash the firmware by running this script (if you're on Linux):

serialDevicePattern="/dev/ttyUSB*"
serialDevices=( $serialDevicePattern )
serialDevice="${serialDevices[0]}"

echo "serial device detected at $serialDevice"

sudo docker run -t -i -u esp \
--device=$serialDevice \
-v $(pwd)/firmware:/home/esp/shared_project \
tavk/esp-sdk:0.1.0 \
esptool.py --port $serialDevice \
write_flash -fm dio \
0x00000 nodemcu.bin

If you're on Windows you're probably best off using one of the GUI tools or creating a Linux VM.