Getting started on greenhouse controller

I was pointed to Arduino for the purposes of building a controller for my greenhouse.

Ideally I need to be able to monitor temperature and humidity. I need to control a standard 24V irrigation valve to regulate the humidity. In the future I might like to control several of these.

Controlling temperature might be more difficult. The greenhouse heater is plugged into what I think is a 240V 20A outlet. I guess I need to put something between the outlet and the heater that can cut the power on and off.

I also need to be able to program in different target temperature and humidity ranges depending on the time of day.

I hope this is the right place to ask questions like this. If not, my apologies. Otherwise, any help is appreciated.

This is not an unusual project. Try Garduino as a search term to see what others have done.