In Lanczos algorithm, can we choose the staring vector to be the first eigenvector of the input matrix A?

In Lanczos algorithm, can we choose the staring vector $$v$$ to be the first eigenvector of the input matrix $$A$$? How can we select it? and why $$v$$ need to have norm 1?

Why does $$v$$ need to have norm 1? It does need to (at least the way the method is usually defined); but typically the very first thing you do in the algorithm is normalizing it by replacing it with $$\frac{1}{\|v\|} v$$, because you aim to construct an orthonormal basis.