Hi Cameron,
Where abouts will you be living?
Sea mounts and coral reefs and the further north you go the better it gets.
I did 10 days north of Santo in the Banks Islands and doggies and GTs were prevalent. Sails, wahoo and 'fin also live around these sea mounts and reef edges.
Also went from Villa to Santo chasing Blues, but encountered same species all the way up.
Give Dave from Ocean Blue a call, these guys have been doing Vanuatu for years.
Cheers
stan