That sounds doable, but don’t get carried away with fancy gadgets first. A cheap humidity sensor and a light sensor wired to a Pi, logged to a CSV, is all you need. Just remember to calibrate the humidity sensor against a known standard, keep the Pi in a thermally stable spot, and make sure the moss isn’t getting too hot from the board’s heat. It’ll give you a neat data set, and you can always swap in a better sensor later if the first round proves unreliable.