Is this project doable for people like me with zero knowledge on electronics? I am afraid of screwing it up during the assembling process…
It’s difficult to say… largely depends on your technical prowess, not so much electronics. Have you ever messed with anything Arduino based or the like?
I have no experience tinkering with Arduino related stuff. 
All of those decent light meters aren’t available in New Zealand, so I’m not sure what to purchase at this stage.
Maybe you can try eBay?
For New Zealand, I found this:
https://nz.mouser.com/ProductDetail/Extech/SDL400
https://nz.element14.com/extech-instruments/sdl400/light-meter-datalogger-2000-to/dp/2688660
https://www.newark.com/extech-instruments/sdl400/light-meter-datalogger-2000-to/dp/06AC2513
(the last 2 websites look identical)
Here’s more: https://nz.rs-online.com/web/c/test-measurement/environmental-test-measurement/light-meters/
Does anyone of any other brand that could be added to the list?
Can you actually use those $25 Uni-t’s to make a runtime graph?
The current Uni-T offerings can do some logging. I also asked them to please consider making one that uses an SD card, and a remote sensor (cabled).