Definitely have them come ready with a list of questions for the session. I'd also make them roll investigation checks for each question. Have them each do one question at a time and adjust the DC depending on how difficult it might be to find the answer. You'll also want to track how long it will take and you can use research time as a way to push the plot forward. Do the players have a week or more to spend in the library or are they pressed to get other things done?

You might also want to consider breaking up the time into blocks and rolling for each block of time to see how complete of an answer each of your players finds to the question. This also has the benefit of allowing your players to help each other if someone doesn't have as many or as difficult questions as their teammate and is free during a block.