In my brief Internet research, I found that this site
recommends ordinarily calling an Orthodox Metropolitan "Your Eminence." The Wikipedia entry for Metropolitan Kallistos
, however, gives his title as "His Excellency." I recommend using "Your Excellency" for Metropolitan Kallistos and "Your Eminence" for most other Orthodox Metropolitans. (Please see the site at the first link for specific information.)
Kissing the hand of a bishop is a recognition of his episcopal authority. Given that the Orthodox have valid orders, it can be argued that a Catholic could choose to kiss the hand of an Orthodox bishop. That said, given the current separation between the Catholic Church and the Orthodox churches, I cannot recommend that a Catholic do so. It seems more prudent to observe the protocol applicable to exalted religious personages whose religion you do not share: Treat them with respect by, for example, ordinarily calling them by the courtesy titles they expect; but do not participate in rituals that acknowledge their spiritual authority over their own subjects. Translated to this situation, that would mean addressing Metropolitan Kallistos as "Your Excellency" but not extending your hands to him.
As a side note, Latin-rite Catholics are accustomed to saying to others, whether they be laymen or clerics, "God bless you." In the East, in both Eastern Orthodox and Eastern Catholic circles, it is considered inappropriate for a layman to offer a blessing -- even if only by word alone -- to a clergyman. In recognition of this point of protocol, I recommend that you avoid saying "God bless you" to a member of the Eastern Christian clergy.