Your fuel usage will depend on your boat and conditions as you could go over in a 12 foot tinny with a 6hp motor if the conditions were flat and you had 1/2 day to get there. But the problem is the weather can change pretty quick and its like 50km across from the port of Brisbane so that's a 100km trip then add 1/3 extra fuel for safety.
If you fish Peel Island or Harries Art or even Mud Island already then there is really no problems with going to Moreton its just further to travel so just pick your days.
Cheers
Brett