Assuming the top would be around 1.5 m long (to seat six people) and 0.7 m wide, I would fail at planing and sawing the ends if the top were to be secured in the front vise; just because they would either be 6 ft up in the air or the work having to be done vertically.

So, here’s an alternative that would save me from the above:
1. Make the top from three laminates. If the middle one was from form plywood, then there would be two flat surfaces to glue the lower and upper components to. The edges of the plywood would have to be covered by a “mitred frame” sufficiently wide to allow cutting the middle piece down to its final size.
2. With all three parts to same size and carefully laid out, with the bottom on top, drill several holes for dowels, without passing the through the top piece.
3. Cut the centre piece down to its final, reduced, size.
4. Place dowels in the upper board; apply glue to the upper surface of the middle on and put it over the dowels; and then repeat with the bottom board. Clamp down.
5. Flatten the top surface, if required, and perhaps also the bottom one.
6. Inspect and realise that the groove (½”) is too wide, attempt to make a ¼” thick solid wood centre board, and find that getting it acceptably flat might prove too challenging.
7. Admit defeat. Wait for a day without precipitation, and create the groove in a solid piece, using a power router – working outdoors.
(8. Review the design)