Sounds good. I’m always a fan of mixed meat (beef, pork, veal) in my meatballs but all beef certainly works.
I also find that having more herbs (Rosemary, oregano, sage are the first that come to mind) also help to round out flavor if you’re cutting salt. So I might add some of those (or experiment with them).
For that same reason, I wonder about the spinach (I don’t usually put that in my meatballs so this is more of an open thought than a strict recommendation). I wonder if that will mute some of the flavors and potentially add water - both of which might make me want to add salt to compensate …
