'm pretty sure that when it comes to matters of doctrine they will say "Yeah, it seems stupid and nonsensical, but I believe in God and I believe that this is what God told me, so I have to have faith that it makes sense." But I guess I should ask about that, just to make sure. Thanks!

I mean, a bunch of my friends are theology grad students/friars and none of them would answer this way. For most of the religious folks I know who have spent time researching their faith (some of whom are converts), doctrine is likely to have persuaded them of the truth of the religion they follow, a la G. K. Chesterton in the quote below:

“This, therefore, is, in conclusion, my reason for accepting the religion and not merely the scattered and secular truths out of the religion. I do it because the thing has not merely told this truth or that truth, but has revealed itself as a truth-telling thing. All other philosophies say the things that plainly seem to be true; only this philosophy has again and again said the thing that does not seem to be true, but is true. Alone of all creeds it is convincing where it is not attractive”

As for the heaven/hell question, in plenty of Christian traditions, Heaven is desired because it's union with God/a properly ordered will/etc, not just a neat place you can munchkin/sneak into. So, imagine phrasing your question about salvation as "What percentage of the people at this college as kind as they should be?" "What's the chance you are as kind as you could be?" "If it's not 100%, what the main reason why it's not and why don't they chance their actions to make it more likely?"

If those questions would make you double take or object to the framing of the question, you may want to change your Heaven/Hell question accordingly.

I did talk with a theology student who had the opinion that everyone is going to heaven because Jesus did on the cross for human's sins. Before asking more specific questions about heaven and hell it's useful to to know the stance of the person you are talking to.

Afterwards you can force them to be more specific and name hard numbers. Pressing a believer into giving you hard numbers can switch them of reciting established talking points.

"Yeah, it seems stupid and nonsensical, but I believe in God and I believe that this is what God told me, so I have to have faith that it makes sense."

In that case I would check how they know what God told them. God directly speaking to them? Them reading the bible? Don't different people interpret the bible differently?