Will, I've found my 8 HP Honda uses very little fuel. It appears to be the trend with the newer four stroke outboards. I use the factory supplied external tank, and have found it to be more than adequate.
If you are to go on a week cruise, you can always tie an extra container to the lifelines.
I also have the same question concerning the line lengths listed in the downloads for my boat. They seem to be very long, compared to what I have on the boat. I'm new to the Hunter scene, but I believe I'll use a combination of what I have and some common sense to sort out my new line lengths, when I need them. As example, I believe the downloads say 70 feet for my jib sheets, on a 22 foot boat. Tied in the middle that gives me 35 feet on each side. I could fly wing on wing with a whisker pole and still have 10 feet in the floor. I'd love to have input from others concerning this info. And I may have my numbers slightly off above, but the order of magnitude is right.
Richard