Yes it is a grade level.
a grade 5 is a hard level
It means that you are grade level c witch is 3rd grade
You do not need to hyphenate.
You do not hyphenate the number.
You would hyphenate "thank you" when it is used as an adjective before a noun, such as in "a thank-you card."
Don't hyphenate; ongoing is one word.
You hyphenate it only at the hyphen.
I think it's more accepted to hyphenate it.
About grade 3.
no its 6th grade level
Ready Level E is typically designed for students in 4th grade. It focuses on developing reading comprehension and vocabulary skills at that grade level.