How many tests are needed for optimal coverage?

Question

Software testing

Good afternoon!
We do some manual testing. We also write test cases.
Also there is, for example, such case:
The form of 27 fields, each field accepts from 1 to 8 values.
I took a pict ( here it is ) described the fields, described the input data.
Added some IFs to describe special situations. (For example, if a certain field is empty, then the "child" field is also empty).
Got 87 combinations of input data. Is this a normal situation?
How many tests do you have on average? And for what functionality?
I understand that there cannot be an unambiguous or even average-correct answer, it's just interesting to know how many tests cost in other projects, and how many 87 tests are realistic for such a form?

Answer 1

And if the form has 270 fields or 270,000,000? :)))))))