Well, here's what I would do,,--, but then, I always over-build. No such thing as too strong.
First that bench needs something, A post/leg), in the center, it will have too much flex as it stands. I would find some hardwood to glue and screw to the underside of the counter top, right where you plan to mount a press. Figure on running the bolts clear through the hardwood stiffeners and the counter top. Bolts, not screws. That takes some planning, be sure that's exactly where you want the press, then re-enforce the underside to take the pressure of the press when FL sizing or forming cases.
You could get away with a pine 2 x4 for economy, but it too should be glued and screwed to the underside.