Answer to 1).
In general, given a linear mapping $$\phi \colon E \to F$$ it extends uniquely to a homomorphism $$T(\phi) \colon T(E) \to T(F).$$ The proof can be made coordinate-free, in fact it follows from the universal property of $T(E)$ applied to the map $$\eta \colon E \to T(F),$$ where $\eta=i \circ \phi$ and $i \colon F \to T(F)$ is the natural embedding.
Moreover, one proves easily that $T(\phi)$ is injective [risp. surjective] whenever $\phi$ is injective [resp. surjective].
For more details, see for instance [Greub, Multilinear Algebra, Chapter III].