It is best to get the most complex piece done first. For this project this is the side supports of each of the shelves. 

These are cut just like you would cut a box joint, only less care is needed to set the spacing as you won't have fully nesting pieces like you have on a box. The easiest way to do this is to use an auxiliary fence on your miter gauge with an indexing block. This is done by first cutting a kerf in the fence using your dado stack and plugging it with an offcut of your side to side slat material. The resulting pin is where you will register each piece for cutting the notches.

To measure the distance between each notch, use one of the strechers to sit between the registration pin and the dado stack. We don't need an exact 3/4" spacing, just close enough for visual purposes. Once you've established the desired spacing, secure the auxiliary fence and prepare to cut the second kerf.

After the kerf is cut, you can begin making the notches in the shelf sides.

If you have a tight fit on your registration pin, take some wax and apply it to the pin. This will help getting the side supports on and off the pin.

Start out by sliding the side support up against the pin, then make your first cut in this position. Once the cut is made, move the notch so it nests over the registration pin and make the second cut. Repeat this until you can't make any more complete notches.

I use a clamp to hold the side support in place when nearing the last few cuts to keep my hands away from the blade.

*I do have a throat plate for the dado stack now, but at the time I was tired of waiting for the shipment to come from my Amazon order.*

Here you can see that my spacing isn't exactly equal, but it's close enough for aesthetics.

When the cuts are finished, I matched pieces and marked them as pairs. You can see I cut 7 pieces, this was mostly for insurance purposes, but the extra piece comes in handy when gluing up each shelf.

Surfacing stock will make it difficult to keep in a sequential order. At this point I labeled the end grain since that will be the last to be trimmed.

I jointed and planed each slat to a oversized thickness of 1 3/4".

Here you can see how difficult it can be to keep sequential order without marking the endgrain.

When thicknessing each slat to final width, use your end pieces to gauge your progress. I went for a slip fit on these joints. Too tight and you risk snapping the side supports, too thin and you'll have unsightly gaps in your joinery of the finished piece. Take great care in this as these joints are a main feature of the piece.

I could have used the planer to take the slats to a final thickness, but the tablesaw was faster for this process. If you have a large floor standing planer, you can do this in 1-2 passes taking off more stock than my planer can. The advantage of this is you'll have a much more finish ready surface than you would off your tablesaw.

Once you're to final height and width, crosscut your slats to a final width of 36" (in my case). 

I should point out that if you take your overall length to more than 36", I would highly recommend adding a center spacer/support piece that you'd find in traditional Nelson benches. Without this you'll have lots of potential flex in the center of the shelf.

Without any markers for keeping order, at this point I set the slats in their final orientation with the side supports. You can use blue tape and numbering to keep order, but I knew that this method would work just as well for me.

For cutting the notches on each of the stretchers I opted to use my flat top ground combination blade. I prefer this method because I get a true flat bottom on my dado/notch. The majority of dado stacks leave a slight 'batman' profile on their cuts due to the pointed carbide teeth on the outside of the stack. 

There is no reason you can't use a dado stack to cut these notches, I simply prefer this method and dislike installing my dado stack.

The first step is to set your blade height correctly. There is an easy method to find the exact center of your stock:

1. Mark the center of your stock
2. Move the blade height to this line
3. Make a cut on the bottom and flip the piece and make the same cut on the top
4. If you have a thin piece of stock left between the two cuts, you need to raise your blade, if you completely remove all material you need to lower the blade
5. You ideally want a paper thin piece left after your second cut, then you know you have the proper height for a half lap.

I used several of the slat offcuts to test these half laps and make sure I had proper blade height set.

To get the proper length of each notch/half lap I employed my marking gauge and the side supports. First set the gauge to the thickness of the sides as shown in the photo.

Take your marking gauge and scribe a line on a test piece if you have them. 

Use the test piece to adjust your miter gauge and stop blocks to get a cut directly on your scribe line. You can see in the photo that the saw kerf did not leave any space between itself and the scribed mark.

Once the length of the notch is established, I used repeated cuts to remove the remainder of the waste material.

Repeat these steps for the remaining 7 slats. Check the overall fit of the shelf, if everything looks good, then move on to the next 16.

Depending on how fast you work, you'll be done in an indeterminate amount of time.

Something to look out for is if you have variance in your notches. Here I ended up getting a bit sloppy and let the stock lift during the cut. This causes a slight gap in the joint between the slats and side supports. 

If you inspect the notched area you can see the ridges that are keeping the slats from fully nesting in the sides.

This is easily resolved with a slight undercut. A sharp chisel takes care of this easily in one or two passes. 

Clean face results in a good seating. 

At this point I highly recommend pre-finishing the interior sections of these slats. Once the shelf is glued together, it will be very difficult to get in between for finish application, especially if you're wiping like I did. I taped off the crucial glue surfaces as shown. The bottom section is endgrain and won't provide much strength to the joint so I didn't waste time masking that off.

It's important to keep order, so I marked the slats again on the glued surfaces and x'd the portions of the side supports that need to get trimmed off.

I trimmed the side supports to their close to final length. I left them slightly proud which I'll trim after the shelf is glued together. 

Here you can clearly see the areas I masked off for gluing. I used an old children's toothbrush because I realized too late that I used my last glue brush on a previous project.

Here is when the extra side support will come in handy. By placing it in the center of the shelf, you have extra support when clamping the front and back slat into place on the sides. Without this piece you run the risk of bowing the material with the pressure of the clamps.  This slides out easily after the clamps are removed post glue dry.

A copious amount of clamps and a slow set glue are key for a good assembly here. 

Before I trimmed off the excess material of the side support, I put down some tape to leave me enough material to clean up with the chisel and get a good surface.

After flush cut and cleanup with the chisel.

Rinse and repeat for all three shelves.