Everyone has their own pace, so there are no absolute “okay or rip” numbers ^^
That said, I’d recommend focusing first on reviews, then doing some lessons when the number of reviews goes down. A good indicator is the number of “Apprentice” items. I’m personally comfortable with around 100 of them, so when there are over 100, I stop doing lessons until that number drops.
EDIT: The ultimate timeline userscript can help getting an overview of your review schedule and plan accordingly: