ishabana:
The project basically should have 3 standalone Arduino boards, each should read a number from an online API, then send it to a center board (Arduino as well but connected to a machine) where I want to do some math with the received numbers, then send to a machine (PC) where I am taking it from there and use these data in other platforms
This is incomprehensible, not helped by the link you posted being unusable. As yet. there is nothing to suggest why you need four Arduinos. Are they remote from each other?
I am a Mac user btw!
I don't think that is a liability in this arena.
First, and since I am looking for a minimal setup, what do you think of this board:
That device has two microcontrollers, and therefore hardly minimal. The ESP8266 is a lot more powerful than the Uno part, which is doing little more than going along for the ride. I can't translate the cost, but I bet it is high, while ESP8266 devices like the Wemos noted above or the Node-MCU are dirt cheap and should be all you need.