Two ways in. Pick the one that matches how you work.
Do more than three fairs a year and the annual licence is cheaper. One booth to design and nothing after that — take the project pass.
No. It runs seven days from the moment you buy it and then stops. Buy another whenever you need one.
They stay on your Mac. The exports you already made keep working — they are plain files.
No. It just saves typing if you already keep your inventory there.