not only . . . but also?

or: "...as well."
The first is a more formal convention, the second less so; which you use would depends on the situation (audience).

Yes.

If you start with "not only", it is perhaps expected that an "also" will follow.
As mentioned, it is a slightly more formal expression.
The whole can be simplified, as in everyday speech, into something like
"She looked good, and felt good too."
But even here, they are interchangeable:
"She looked good, and also felt good."