In Doctor Faustus, in the section you provided, Faustus appears to be not only a learned man, but one who is familiar with good and evil.
Faustus shares his perceptions of damnation. First he notes that Faustus, speaking of himself in the third person, is fearless; damnation does not frighten him, Faustus.
For he confounds hell in Elysium...
eNotes.com translates this to mean that Faustus thinks little of damnation and is therefore "indifferent" to being in hell or the Elysian field (where, in Greek mythology, the righteous and heroic would spend eternity).
Faustus believes the Devil and old philosophers are together in hell, where he, Faustus will also be: so it would seem Faustus believes that philosophers of an older time ended up in hell, perhaps because they turned their back on, or questioned, religious doctrine.
Faustus then goes on to question Mephistopheles about his "boss." Here Fautus and Mephistopheles recount the Biblical story of Lucifer's fall from heaven.
All of this further characterizes Faustus' clear knowledge of exactly who he is preparing to serve, in complete rejection of his faith in God; but he does so very analytically. He is not calling on the powers of darkness in some emotionally charged state, but he is very precise and studied about it.
Mephistopheles points out the sins of Lucifer:
O, by aspiring pride and insolence;
For which God threw him from the face of Heaven.
In this way, Faustus is being reminded of what can take the most righteous of beings (angel...or man?) and throw him into the fiery pits of hell.
Mephistopheles then goes on to say that he and those like him who supported Lucifer are in hell, which is everywhere God is not.
Why this is hell, nor am I out of it:(80)
Think'st thou that I who saw the face of God,
And tasted the eternal joys of Heaven,
Am not tormented with ten thousand hells,
In being deprived of everlasting bliss?
O, Faustus! leave these frivolous demands,(85)
Which strike a terror to my fainting soul.
Surprisingly enough, Mephistopheles seems to be lamenting his life in hell--perhaps hoping Faustus may change his mind. Faustus' "frivolous demands"--his questions to Mesphistopheles--are causing agony to Mephistopheles who suffers by having known Heaven and by now being evicted from it for eternity.
With all of this in mind, if I were writing about the characterization of Faustus, I would describe him as an intelligent man who is familiar with the doctrine of the Church. In a very logical way, he collects further information from Mephistopheles about Lucifer and hell, preparing to make a well-researched decision. Ironically, as with the old philosophers, it seems that he is preparing himself to join the ranks of those who serve the Devil.