You would not say someone is a hit star. That would seem redundant. A hit in this context means a success, a great success.

There are a few times when you cant add the word to another, but not many. I will gave you a fun one. It is called "A one hit wonder." This is when a stare is known for one song. Some musicians or singers have only one good song that makes them famous and they can not recreate the success. Another example is called a "Smash Hit." This is a song that is doing very well in sales and is played on the radio all the time. This is also called a "Hit Single." If a record is a hit, it has the term "a Hit Record." But that does not apply with a movie.... Besides these and a few others, Hit stands alone. Have a great day.

Yeah, you can use "hit" to mean popular, but it's a noun, so you have to say "this movie is A hit." You can't say "this girl is a hit star." Most of the time you say big and hit together.

Hit in slang means a popular phenomenon (pop culture), "blockbuster", eg you could say, the Batman movie was a "smash hit".