To be honest, I’d start with using a NodeMCU as your replacement for the Arduino/ESP-01 combination.
The reason being that the NodeMCU has a built-in TTL to Serial adaptor, which is easy to access via the onboard USB connector, and it has lots of useable GPIO pins. It’s also much easier to flash, as you don’t have to mess around manually putting it onto flash mode by pulling GPIO0 low.
The ESP-01 on the other hand is trickier to use as it has no TTL to serial adaptor, limited GPIOs and is more difficult to flash. The adaptors shown in the article you linked solve some of these issues, but not the limited GPIOs.
If you work with the NodeMCU first then getting it working will be much easier, and you’ll have good access to the serial debug data. If you then want to do the same thing with the ESP-01 the what you’ve learned with the NodeMCU will be helpful and make your life easier.
You should also read this:
Pete.