It depends on the base but usually the odds of breaking guarantee are slim. I've never broken guarantee or even been close. One month on reserve I blocked 2 hours.

You can pick up trips on your off days as long as they don't conflict with your reserve duty periods or reserve assignments. Those trips go above guarantee so if you fly 2 hours total on reserve and pick up an 8 hour local on your off day you'll get paid 75 hour guarantee + 8 hours.