Hi Lundin,
Thanks for your reply. It was great to get some suggestions for solutions for the PH measuring. And I see that a temperature sensor seems to be included in the basic Arduino starter kit, so that seems to be sorted too. I'll let my husband see the links for the PH-meters you recommended, so he can make the decision later on. I guess it's good if we just get started with the basic kit and don't get into deeper waters until we're a bit used to things...
Yes, I suspect the programming should be the fun part - that is for my husband. I'll let him have a proper go before I try my hand at it. 
Thanks again.