This took a while! I spent about an hour making the jig, and at least another 3 hours on the stairs. The jig is made of scrap chipboard and museum board. I measured the width of the steps, and subtracted the thickness of four layers of cardstock, since each of the stringers is two layers thick. It was worth taking the extra pains to make the jig, since I'll use it to make more stairs in the future.

I didn't use a center stringer -- I printed two stringers, fit them into the jig and then glued the steps to the stringers. Then I made the railings and glued them to the step sub-assembly.

All edged with neutral grey gouache, as usual...

https://twitter.com/ridetheory/status/885268105651298306

Your technique is flawless. Sorry I took so long to respond.still getting used to my phone.