I'm just trying to figure out the best way to get the most support without having the joints coming together unevenly.
If you have a biscuit joiner it will take you 1 minute to make the joint.
You didn't mention what kind of fasteners you are going to use to secure the shelf to the brackets. Because you posted that picture, I figured you might be looking for input on that.
I would either sink bolts into the top of the shelf (optionally fill with a piece of dowel rod for looks) or drive t-nuts into the bottom. Depending on the thickness of the shelves you have to work with, you can get low-profile bolt heads if you must. Home Depot and friends might not carry many fasteners, but you can get elevator bolts from Fastenal for a reasonable price. They are flat on top.
Also if you are planning for the shelf to go all the way to the wall, keep in mind that customers of the shop will be handling the items on the shelf all day. It will have some forces applied to it! Not only will this pull on the hangars, but if the shelf goes all the way to the left wall, it will bounce against it and eventually damage the wall. Think about leaving a small gap there, or putting some cushion on the end of the shelf, so it won't mar the wall.
Lastly, I'd make sure those brackets are secured to the frame of that wall. If not, you will eventually have to make repairs, as children do things children do when they are in public. I'm sure we all climbed on something our parents told us not to.