While what your company is doing is commendable (most don't pay extra or rotate in that fashion) #3 is a red flag for me because it sounds like the overly friendly but in the end passive aggressive and unprofessional atmosphere I've witnessed at startups and midsize companies who pretend they're startups. If on call is optional what's with the social penalty for people not wanting to do it.
IMO what companies should be doing is paying extra per hour until they get people that want to do it. As in, increase the price they pay "extra" until someone decides to give up their free time outside of normal development hours.
IMO what companies should be doing is paying extra per hour until they get people that want to do it. As in, increase the price they pay "extra" until someone decides to give up their free time outside of normal development hours.