If you want all of your characters to share the same rig then the base of each of the characters should all fit on the same rig to start. You can then create a component character of the 6 foot 3 character and another for the 5 foot 8 and scale the relative size using whatever you set up as the root object in the component Character BP. Straight answer is yes you can use one rig.
Also facial expressions is not the same as lip sync and only require a single pose frame so you could make a set for each possible expression and add them as an additive on a per bone layer.
Quick test done using clusters and a single layer.
Still need to add the expression and eyes layer that I’m thinking of doing procedurally.
P.S. Since a cluster is just another bone it can be animated just like any other joint in Persona.