We just selected Freshdesk as our customer service tool. We based the selection on the fact that overall it seems to have the best looking UI, and has good integrations. Overall, it checks all the boxes. We liked the ability to integrate ticket submission into our own application.
We use Bill.com is for our accounts payable, although we just started with it this week. It will manage our approval cycles and payments, and it integrates well with QuickBooks.
QuickBooks Online is our accounting system. QuickBooks makes it easy to collaborate with our accountants.