As it turns out, a former question about the MoveTo not working with pawns had the answer nestled within it all along: Behavior Tree MoveTo not working - #10 by perryMUFC92
Specifically, my Target class needed a custom PawnMovementComponent that reimplemented the RequestDirectMove function that MoveTo relies on to do its work (the answer from perry says the class needs to be a NavMovementComponent, but PawnMovementComponent works fine for me as long as that function is implemented). I stumbled upon NavMovementComponent with Pawn in UE4 - Won Bin -John- Kang that gave a pretty good base for how to set up the component, and then I just applied it in Target.cpp like so…
TargetMovement = CreateDefaultSubobject<UTargetNavMovement(TEXT("Movement"));
TargetMovement->UpdatedComponent = RootComponent;
and then just had to set the damping to 0 and the box is moving point to point as expected! SelfActor is still set to None, but I guess that wasn’t really the problem here.