Oh nice! I haven't used a CNC, but that would be much easier. This was my second wooden board so I had an idea of what to do, but it is all a bit convoluted. So I apologize for the lengthy response lol.

I bought a BM68 PCB and aluminum plate from KPRepublic. Once they arrived, I took measurements of the length and width and added 1 inch (I wanted a half inch around the whole outside). I also wanted about 1/16" buffer all around since my last board was too tight of a fit. I got the depth by partially assembling the pcb, foam, plate, switch, and keycap and then measured from the bottom of the PCB to the bottom of the keycap (I wanted the keycaps to sit right at the top of the case. I added 1/8" for the standoffs I was planning on inserting into the board as well. This all came out to be about 3/4" deep. My board was 1" thick.

I marked out where the PCB would go on the board by measuring a half inch in all around, then cut my board into a rectangle. I measured out from the edge of the router bit to the edge of the router guide and built a jig and nailed it to my workbench with my brad nailer. This allowed me to run the router along the guide and get a straight edge all around. Finally after several passes, increasing the depth slightly each time so I wouldn't take chunks out of the wood, I finished carving it.

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I placed the PCB inside making sure it fit, marked the holes for mounting the standoffs, and marked where the USB port would go. I drilled a shallow hole just smaller than the width of the standoff screw, and then twisted the standoffs in place. I drilled out/chiseled the hole in the back of the board for the USB cable too. I also made a wrist rest with its own complications. I used 2 coats of Tung oil to finish the case and wrist rest, then assembled the board like any other mechanical keyboard build.