what if i want to reset >1 device with the manual reset.
Beware, some '51 derivatives OUTPUT a reset on the reset pin umder certain circumstances.
do i have to buffer the output
With what?. The reason to use a supervisor rather than some schmitt trigger is that the suoervisor is specifed from close to 0 volts whereas your "buffer" probably will not be specified at less that 2.5V

Erik

If you are doing a careful board layout and all your devices are CMOS, you can handle the above with 1k series resistors (and, in some cases a diode or two)