This sums up the Barbarians from Lv 10 - 19 it shows that they will attack and Resources needed for a Ceasefire as well as:
their willingness to attack you
Time to rebuild
and resources you can pillage http://ikariam.wikia.com/wiki/Barbarian_Kings/10-19
I hope this answers any questions you may have about proceeding to Lv 10 Barbarians.
(n) The tendency not to start anything until you've had a cup of coffee