I'd like to swap out the wingpanel at the top of the elementary screen with the XFCE motif. Can someone direct me on how to do this? Thanks.
What you are asking, can be achieved using a custom desktop session. Pantheon, xfce, lxde, unity are all window managers which run inside xorg sessions.
So, in-order to use xfce motif top panel, you need to replace wingpanel(elementary) to xfce4-panel in a custom desktop session.
To know in details about Xorg : Xorg Debian Wiki
Details on window managers: Display Managers
This blog might help you find what you need: Custom Desktop Session
If you just want an icon theme to make your elementary look like xfce: elementary-xfce
Or if you want to retain the default pantheon-wingpanel but want to customize the style: Customize elementary wing-panel