@Yveaux thank you for your help! yes, that makes a lot of sense actually. My ignorance on the matter kicked-in once again... sorry
What I'm missing so is how to create a sensor node which can be operated on battery and take measurements every "x" seconds/minutes/hours: shall I leave the Gateway always on and then configure differently another Node-MCU to act as a Sensor Node ?
Edit: In fact all of this was meant, for me, to be a "test run" bedore developing the whole system. I got a little off-road with the deepSleep and Battery thing, but I wanted to have a real-word-test of my sensor left for a day in the soil while sending reliable data to controller. As I'm reading even more documents and forum post, it's getting clear to me that the best thing would be "ask to the comunity" their experience with HW nodes, thus I can decide which one is best for my case.