Hi Kenny,
In general, there should be no issues opening Quick Fields 8 sessions in Quick Fields 10. However, we have seen some people run into issues if their Quick Fields 8 or 9 sessions use process profile permissions. If this is the case for you, you can remove the process profile permissions from your session or wait for an upcoming update for Quick Fields 10 that will resolve this issue.
To answer your second question, Quick Fields Agent is not dependent on the Quick Fields Server. If you have the Quick Fields Agent add-on, and you select the Quick Fields Agent check box during installation, Quick Fields Agent and the Quick Fields Agent MMC Snap-in Administration Console will be installed. Keep in mind you can also install and use the Quick Fields Agent Web Administration Console to administer Quick Fields Agent.
Let us know if you have any other questions or issues.