I first thought Will was an INTP, given his private intellectual nature and actual interest in some heavy, heavy reading (e.g., Nietzsche, Kant, etc.). However, I now think he's most likely an ENTP. He's witty, charming, funny, dominant, rebellious, troubled, intellectual, and social. He may be very low on extraversion, though. Either this, or an INTP with an unusual amount of social interest and ability. But yes, he mostly seems to be a somewhat nerdy ENTP. The guy's Ne is off the charts. The scene in which Will is explaining why he doesn't want to take the government job is nothing less than the use of Extraverted Intuition to understand the big picture from a global perspective (though no doubt Ti is also at work piecing together all this information). It's complex and intricate, like a giant web of thought.
So yeah, that's my verdict. ENTP.
Personally I think he's an INTP
the major question being, is he an introvert or extrovert. While you could say extrovert due to his interactions with his friends, and his charming nature; I would say Introvert because a lot of that is part of his protective emotional barrier.
ENTPs can also appear introverted due to protective emotional barriers, as well as not caring as much for other humans due to some level of resentment. Not all ENTPs lack emotional barriers due to damage, and not all ENTPs enjoy being around people. Some actually find people extremely annoying and prefer to spend lots of time alone (though they are definitely not introverts). So this reasoning does not work.
ISTP??????? Hellz no, not even close dude; Too charming for an INTP, too intuitive to be a sensor (not merely intellectual, capacity but the way he sees things as a whole in part of a bigger totality, his ability to size up people accurately, and he has a strong NT, and is blunt; could be a J, but I doubt that too; he seems to be very much able to be quick on his feet and adapt, intellectually-speaking and through his manerisms.
Yup. He's too charming to be an obvious introvert, and he's definitely not a sensor since, as you said, he's capable of seeing the big picture with extreme capability.