FF14 uses around 233MB (With Dungeon Runs)
Most MB ussage is chat funny. If you stand aroun din Mor Dhona all day, you will have a painfull high Volume at the end

Ping is around the same as PC due to the fact servers for europe are so strangely placed.

EDIT:
My Source:
My Own Experience due to me playing with Broad band from Military Barracks