I don't really have any advice, just a comment. I do use the auto-focus feature, but it always ask myself why. Personally, I do not know why I do not take over the focus myself. I just feel the camera Sheldon knows where the focus point is and I hate when I have to fight the thing to focus at the correct point.
I did not read up on the lens, but can you play around with your current lens in a manual focus mode to get a feel for it?
I think I am saying you seem to have a good eye and I think it is something you would get comfortable with rather quickly. For me, I find in a theme park setting, there are often items in the field of view that you really aren't trying to focus on anyway and the auto focus can easily pick the wrong subject.