«Πόσες ὑπάρχουν οἱ θεάσεις»;
Πόσες θεάσεις υπάρχουν, this is the proper Greek syntax. No article here, as it is in English, it is indefinite noun. Instead είναι goes with an article.. Είναι and υπάρχουν seem to have the same meaning here, there are, but their use is different.
In reality no-one says θεάσεις though... Everybody says βιουζ.
I'd say that most people say προβολές. Θεάσεις is another thing and not used for that. In the new tree we have taken care of these problems.