Once I got the legs knocked together, I fitted the leg tenons and so was able to mock up the bench assembly.

With the stretchers in place I clamped the piece for the top to the legs using the holdfast holes, this let me plane the front edge of the bench top.

Once I got the bench top edge flat I turned to the stretchers and chopped the narrow mortices for the wedges.

With the wedges in place the whole undercarraige stiffened up tremendously.
The leg assembly being hopefully in its final place I made the peg holes to locate the top.

Finally the I flattened the top with my scrub plane, toothing plane and try plane, using the toothing plane set a little finer to give the final surface a bit of grip.

The sapele tore up quite a bit with the scrub plane/try plane combo, hence the switch to the toothing plane.
The cross grain scratches from the toothing plane stop the try plane from lifting a shaving, thus preventing tear out.I used the same technique when I flattened my last bench.