I AM SO HAPPY! I have found solutions to both of my problems.
The fix for the RPCs was simply selecting File/Refresh Visual Studio Project in the editor when any new RPCs have been added.
The fix for the replicated UPROPERTIES was adding this to my .cpp file, including a separate DOREPLIFETIME for each replicated property:
void AClass::GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& OutLifetimeProps) const
{ Super::GetLifetimeReplicatedProps(OutLifetimeProps);
DOREPLIFETIME(AClass, ReplicatedProperty);
}
Thanks again to everyone who shared their input.