Here's the full sequence of assembly:
The cross pieces fit into the mortise holes in the sides
You can see that I opted for a protruding through tenon (or whatever the analogous term is for the insert part of a bridle joint). This is partly an aesthetic design feature and it also means that the joint will allow for a little expansion or contraction of the wood without leaving an unsightly hole or protrusion. It's hard to tell from the pic but I chamfered all the corners of the tenon.
Next, a 90mm connector bolt gets driven through the lined up holes in all the pieces and into the cross dowel in the screw strip, securely pinning the bridle joint in place.
Here you can see an inside edge of the leg with the strips that will support the base. The little notches accommodate the supporting strips that run front to back along the underside of the base.
The middle legs also have connecting bolts that screw into cross pieces that are fitted with cross dowel barrel bolts.
The top cross attach the same way as the bottom ones
These are the holes in the side panels which lead to the insert nuts in the screw strips that I pictured earlier
The top of the stand gets slotted into place and then the bolts get driven through into the insert nuts in the screw strips
And here's the (almost) complete stand structure. One thing that's missing is that the base isn't currently in place. Ordinarily the base would be fitted in before the top and attached to the sides in a similar way, but due to some minor alignment issues with the holes I needed to make some slight modifications so it's not included in this shot.
That's as far as I've gotten so far. Next up I need to build the doors, install some edging on the plywood top and then prime and paint the whole thing.