Make the top of double or triple thickness of plywood or MDF with
replaceable1/4 masonite over it, edge with hardwood. That's all the
weight you'll need.

Triple is overkill (remember this is not a traditional WW bench) but double
is nice. make sure that you have a ~2" overhang with the full bench
thickness. It's nice to be able to use that edge as a clamping space. If you
had (for instance) a 1" thick top with 3/4" thick by 2" apron/edge it would
make a lousy clamping surface.

I would move the metal vise to the left a bit and have it closer to right
over a leg.

What's with all the knee space? One "desk-like" space is nice to have, but
unless the other space is specifically reserved for the shop vac or a trash
can, I say: fill it all with drawers.

A few words on drawers.... don't make them all the same height. 2" of usable
depth is good enough for screw drivers and wrenches. 4" for hand drills,
more for things like routers. You will want a mix.

-Steve