For the size you're considering, half inch BB ply should produce a nice result. The nice thing about BB is the multi-layer edge is nice looking, colorful when rounded over and with a clear finish. Good side up. It will make your other wood stuff stand out.
You can cut a lot of it with the Circ saw, the notches with the jig saw. Someone pointed out that you use the vertical back leg to lay out the notches, that way, whatever angle you settle on, the shelves will be level.
I think I'd lay out the triangular piece on a nice square chunk of cardboard, including where the notches will go. If it goes on a table top (I assume it will), I'd make the lowest shelf that same distance from the table top as the space you decide on between shelves. That way the table can hold stuff.
When we set up our display, we need a nice spot to put paperwork, signup forms, extra pens, order forms, etc.
Did you arrange for credit cards yet? We started with BofA, but now my daughter is using something much cheaper - no monthly service fee. It will help, and people bargain less when you accept CCs.
We used to rely on standard folding tables for display, but later we started using some folding tables we found at Target for about $20. They don't weigh a ton, are pretty cheap, come in a box you can reuse. They are much narrower, about 4 ft by 20 inches. We always found that we did better when we arranged the booth so people stepped into it. The thing we hated most was hauling around anything heavy.
Put a price tag on everything and price it a little higher than you usually set. Perceived value is good.
The more I do, the less I accomplish.