In the Cities step, pick All or nothing (the tour goal counts every pledge; miss it and nobody is charged) or Each city on its own (a city that reaches its ticket number gets its show even if others don't).
At the end date each city is decided on its own. At 100% it's confirmed, and its ticket backers are charged and get their BCKSTG Pass. At 75% to 99% it's your call: confirm it, extend it once, or let it go. Under 75%, nobody in that city is charged.
Date and venue can be TBA. Pass holders get an email when you change them.