I have been looking for a general audit checklist since one hasn't been provided by the auditors
That is disappointing. I did this for quite a few years, and it was common practice for us to provide a detailed overview of what would be assessed and why (methodology). We submitted formal requests for information, provided tools for the IT staff to run and collect data, including any potential impact of the collection process (if any). We also had to schedule meetings complete with detailed agendas, which usually meant they knew what to expect. There's no constructive purpose served in sandbagging someone in an initiative like this. Issues are usually aplenty, and most IT staff are open to discussing them if the engagement is kicked off properly.
That said, there are plenty of checklists out there if you look. But the primary goal of this effort should be to surface as many issues as possible, prioritize them, and develop action plans for remediation. I wouldn't be too concerned about being "prepared". Since you have started recently, there should be an understanding that the place didn't fall apart overnight.
If the network that you acknowledge is in need of improvement receives a good report, that would probably be a waste of the company's money.