My suggestion would be to build the Bench just like you'd do a Kitchen Counter. I'd find some used or cheap Kitchen Cabinets and use a Formica Covered Counter Top.
I personally don't really like presses directly mounted to the bench. My Rockchucker is, but the rest are mounted to Aluminum plates and can be clamped to the bench with C Clamps when in use and stored covered off the bench. In your case with 24 feet available, I would consider bolting to the bench but you'll also have enough space to mount them to plates or chunks of Plywood so you can store them inside the cabinets.
Nobody can use all of his presses all the time. As a result they sit idle for periods of time and collect dust and dirt. Dust and dirt are the main enemies of machinery. Keeping them inside a cabinet covered with a Plastic Trash Bag is the best way to keep your tools nice forever. Unless your shed is air tight, dirt will get in, and it will find your machines.
The advantage of using a Formica Counter Top is that nothing sticks to the formica. It can be cleaned with soapy water for dirt or Acetone or any other solvent for greasy stuff. It is available in many colors and the Butcher Block wood grain style lends itself well to work benches. Also they usually have a raised and rolled front edge which prevents things like tools, bullets and other round stuff from rolling off the front, and they usually come with a Back Splash already built in as well. All the benches in my Machine Shop are covered with Formica and have been in service now for 30+ years.
If the counter top is not fully supported by cabinets full length then using 2 2x12's under it will make a rock solid bench.
Cabinets can be spaced as needed to support the counter top and then leave spaces between them for your leg access as needed.
In any event you really need to sketch up some ideas you have, and think it out long and hard. If you are going to all the trouble of building this thing,,, It kind of needs to be right. Just building stuff on the fly is for amateurs and seldom comes out nice.
My .02
Randy