So would you say there are better solutions to building a soil moisture monitoring for many plants ol the cheap? For me, it’s mainly for fun and making sure I don’t miss watering my plants at home :)

Nice! How long should we expect the 2xAAA batteries to last? Of course depending on quality but more than a year?

Any idea what is needed to get MySensors to work with the new NEEO home automation system? Would it be even possible or would we need to go "via" another Controller such as Home Assistant or Domoticz?

Neeo consists of both a brain and a remote. However, it's custom so there's no USB port on the brain.