I haven't worked much with MDF or particle board - simply because I don't like it - so I can't really comment on it because my preference is toward plywood or solid wood (see more below).
I built my combo workbench / assembly table / outfeed area of 2x6 lumber with two layers of 3/4" plywood screwed (not glued) together then screwed to the ends of the 2x6's. I also used a sheet of hardboard for a work surface that can be easily replaced once worn or damaged. My entire unit is of simple construction and it is screwed together without complex joints or adhesive.
For the unit you plan on building, I would recommend screws in lieu of staples / brads and even with glue the bond can be somewhat marginal particularly on the ends and edges of plywood. In regard to the castors on the base, with the construction illustrated, I am not sure I would feel good about the portability of the unit, though it may be okay if left in a stationary position.
My preference for cabinetry and other purposes is generally Baltic Birch, though I obtain my 5x5 sheets locally at a quite reasonable price and quite comparable to the price to the hardwood plywood available at the BORG's and it is much higher quality.
Where are you located? If possible, I would try to find a quality lumber yard where you can often find a higher quality product than available at the big box stores and many times at a better price for what you get.
What are your intended uses for the workbench? I presume a miter saw or such in the middle? There can be a multitude of alternative plans to be found online, though the one you have chosen may be best for your purposes.
I have a couple workbenches that I bought at a yard sale a couple years ago which have a metal frame with a particle board work surface and shelving ( https://www.harborfreight.com/multip...ght-60723.html
). They were in like-new condition and I bought them at a yard sale for $30/each. They have been good for what I use them for in the mechanical / vehicle area of my shop but the shelf on the bottom will sag if much weight is left on it.
I also had a metal frame / particle board shelving unit and while it was rated for 800 lb/shelf (4,000 lb overall), I noticed the particle board soon begin to sag at a fraction of the rated weight - then when I started to remove some of the items to lighten the load, it collapsed into an immediate mess (fortunately most items survived with only minimal loss). I actually bought two of the units at Lowe's and they took both the unit that collapsed and the unit that I had not assembled as a return without any problems even when told that one unit collapsed (I continue to like Lowe's as well as their veterans discount). After looking at shelving from a variety of sources, I chose to instead build a unit out of 2x4 dimensional lumber and plywood.
Previous comments about moisture and particle board are correct and the two do not go together well. I have both a radial arm saw and a B&D workmate that had particle board tops that were damaged by moisture. The RAS had a 1" thick top and after much searching I found a one inch thick 4x8 sheet in a clearance section at Menard's at a dirt cheap price (they don't stock it and i'm not sure where they obtained it) but it can make for a sturdy and flat top - when well supported. I haven't replace the workmate top and will likely use plywood when I do (likely Baltic Birch).