About the engine oil

I would not switch to zero weight oil. Why would you?

That’s what it calls for. Check manual and oil cap

If it eats oil like ours does you will be using 15w in summer. Zero weight was to lower mpg for testing. Way too thin.

Are you using a full synthetic oil? Recommended oil change is 10K for synthetic. I would stick with the 5w-30. I don't know why someone's car is eating oil. They have a problem with something if it does. Perhaps an oil leak or an engine problem, I have had a 2003, 2004, 2011, 2012 and now have 2 2017 Toyota Prius, none of them have "eaten oil" perhaps that owner did not believe in recommended oil changes.

The issue with using oil with the Prius is well known. We changed the oil often and used synthetic. Now we just check the oil level more. Like others have said that they have never had an issue that was the case with our other cars. The 2012 Prius has been the one that has used oil. Older versions didn't.