Yes, your iMac will communicate with your Windows PC, presuming it is running a recent OS (Windows 7 or later). While there is a version of QuickBooks for Mac, you will probably want to run a Windows environment on the Mac (which it can do) in order to run QuickBooks for Windows on it and keep the versions on the PC and the iMac compatible. I believe Crossover can handle this, but you may want or need to just install a full-blown Windows environment using Parallels or VirtualBox (et al).
The biggest "pitfall" of using a Mac in an office is that users generally wonder why they didn't switch years ago, find substitutes for their old Windows software and eventually turn the office into an all-Mac operation, which can get expensive.
Macs and Windows PCs can share networked printers and files.
The only significant problem I've had is when copying files from PC to a shared folder on the Mac. Using the Mac "Guest" account the files are created with owner "nobody" so they cannot be accessed on the Mac without manually changing ownership.
Pulling the files from the Mac from a shared PC folder works fine, this only happens when "pushing" them from the PC to Mac.
There is theoretically a way PC can log into a non-guest Mac account but I can't figure out how.