After several iterations, I've created a PCB to neatly connect the Raspberry to the relays/sensors, I have also added 8 push buttons that can be programmed to conveniently activate the relays. I called it the "Irrigation Hat": You can have a look to the video below which describes the board and all the steps to setup the Software and make the initial configuration:

https://www.youtube.com/watch?v=ohQP0re0zxA

The Board is available for sale at the following link:

https://www.tindie.com/products/angelova/irrigation-hat/

Buying the board can be a great way to contribute to this project.

I want to clarify that the hydrosys4 project can still be implemented without any custom board, all the supported hardware configurations/connections are described in the website.