its unlikely the wifi would interfere, unless the PIR is very close to the wifi unit.
as for the bell box, depends on what it is and how its wired, most modern bells are happy with 12V to them, but some can be placed in hold off first and then have the power disconnected
as for the bell box, depends on what it is and how its wired, most modern bells are happy with 12V to them, but some can be placed in hold off first and then have the power disconnected