Hi,
Priorities:
1. Like you said Pay Roll
2. Getting the database in Quickbooks done, vendors and employees, put in account information for payments received and payments sent etc.
3. Payables - Hopefully he has given you the invoices
4. Receivables - Hopefully you have a list of vendors
5. Past tax information - Hopefully you have at the minimum the past 3 years.
6. Take a break

7. Create a daily log for your review and review it daily.
That is what I would do. I hope that helps.
Andrea