The cuspidal representations of $GL_n(F)$ a non archimedean field $F$ with ring of integers $o$ can be classified by inducing irreducible representation from $Z GL_n(o)$.

The general question:

How does the representation theory of $GL_2(F)$ and the representation theory of $GL_2(o)$ affect each other?

Uri Onn has shown that the irreducible representations of $GL(2,o)$ will depend only upon the residue characteristic.

Does the representation theory of $GL_n(F)$ only depend upon the residue characteristic? Is there a connection to the reduction steps from local field of characteristic zero to fields of characteristic $p$ (e.g. as in the context of the Fundamental lemma)?

In Stasinki "Smooth Representations of $GL(2,o)$" the representations are partionated in to similarity classes of $2 \times 2$ matrices over the residue field (pg.4419) via applying Clifford theory.

What irreducible representations in Stasinski are important for describing the cuspidal representation of $GL(2, F)$?

A little more general, I know that the irreducible dual of $GL_n(o)$ is far from being classified, so to what extent is the irreducible dual of $GL(n,F)$ described in Bushnell-Kutzo "The admissible dual of GL(N) via compact open subgroups".

Is the classification of the irreducible dual of $GL(n,F)$ known only modulo the representation theory $GL(n, o)$ or do we know all the representations of $GL(n,o)$ needed for the dual of $GL(n,F)$?

If the description of the dual of $GL(n,F)$ is possible independently of the dual of $GL_n(o)$, there is a natural last question in the context of Silberger "$PGL_2$ over the $p$ adics", where he classifies the irreducibe of $PGL_2(o)$ via the restricting the irreducible of $PGL_2(F)$.

Can we classify the representation of $GL_n(o)$ by restricting the irreducible representation of $GL_n(F)$?