I am about to upgrade to Windows 8 Professional however I was wondering if I would be able to downgrade to Windows 7 if there are any compatibility issues and such forth.
If you are upgrading a existing Windows 7 install you will still have your old license, you will need to re-install windows in the process of "Downgrading" so it will not save your settings like when you upgraded.
In the past I have been able to downgrade by creating a system restore image when still in Windows 7.
Creating one can be done as explained here: Back up your programs, system settings, and files
Restoring it when you want to downgrade is explained here: Restore your computer from a system image backup
Note that restoring a system image will remove any changes made since the creation of the image. Therefor make sure to store important data on a different partition and back it up before proceeding with the system restore. Also note that it may take a while to restore your system. However, it will automatically restore your computer as it was before the installation of Windows 8.