Anything you do to frustrate your customers is going to cost you a customer. While many people (myself included) swear by password managers for websites and do come up with some rather complicated ones, the majority do not and won't. If they see you forcing them to change their password, or come up with a complexity they don't like, they'll leave.
Again, look at the example of the major sites and go from there. Yes, there are a few that require password changes, but most do not, and for a reason. Customers tend to just simply walk away, with their pocketbooks in hand.