Hi,
Beginning 2020, I have decided to evaluate Smart Home application to find one to fit my needs.
One of them was OpenHAB 2.5 (Synology package). I played with it and in October 2020, I have decided that this one was the best one for me. Knowing that OpenHAB 3 was going out, I waited beginning 2021 to start a new installation.
I have read a lot and I would like to thanks OpenHAB community / documentation as you can find whatever you want even if it takes a little bit time.
A special mention to @rlkoshak even if I do not understand everything on your tutorials 
I spent time on it from time to time (free time is a scarce resource), so I do not make fast progress… But as a beginner, I will do it step by step.
Current installation:
–OpenHAB version: 3.1.0
–Server: VM Debian Buster
So, in order to process, I divided it into 3 differents phases:
*Phase I: Back-end configuration (Things, Model, Channels, etc.)
*Phase II: Automation (rules, scripts, etc.)
*Phase III: Front-end
Phase I is almost done (95%)
Phase II is starting
Phase III, no idea when I will be able to do it! 
In order to summarise phase I, I think a graph will be more self explaining:
Overview.pdf (76.6 KB)