Create custom shortcuts and assign them to F keys
First of all, You don't need Karabinier to change F* keys behaviour. It can be done in Preferences -> Keyboard -> Use all F1, F2 etc. as standard function keys.

Then to assign keyboard shortcut to Terminal You have to switch to Shortcuts tab, select Application Shortcuts then click + sign. There You can choose application in which this shortcut will be working. There's also text input to enter Menu Item name (for example: Close, Minimize etc. check how it's named in Your Terminal app). 



NOTE: There's no Maximize Menu item, I can find only Close and Minimize.
If You want to install 3rd party app for this, I'd recommend Better Touch Tool where You can set a lot more actions to keyboard shortcuts and mouse/trackpad gestures. Here's an example for BTT:



Picture 1 taken from osxdaily.com