All carts made to identical dimensions, and some sort of clamps to hold them together in alignment when you use it as a bench. Sawdust gets into any open constructions, shelving open drawers or doors, so I'd make sure drawers and doors enclose everything. Use plastic windows in the doors so you can see what's inside. 24x36 inches top would give you a 2x6 ft work surface. Later, when you build a serious workbench, you repurpose the stands for a drill press, small band saw, sander, small jointer or planer. I have a couple of steel stands I've enclosed that are similar in form and very handy. One is open (router table) the other is enclosed for storage of 18v tools. It needs a few drawers, but never got around to it.
I have two areas with wall shelfing. One is wire shelving and is fairly deep, and it holds identical size plastic tubs with lids and labels on each stating what's inside. On the other side are open shelves. Keep open shelves shallow (7 and 10 inches deep) so I can't stack things in front of unrelated items. Just my take.
The more I do, the less I accomplish.