Do you intend to produce many of these to close tolerances? Since they're mostly decorative you could just rough out the majority of the material with plunge cuts and a parting tool, then smooth the steps with a file and emery tape. If you need to keep close enough to a plan for some reason you could figure out how far to plunge each step.
Here's a shoddy representation.

Although the way i'd do them would just be to cut the bulk material free hand with the carriage and crosslide handwheel and file it smooth.
I know there's a great temptation to try do everything in clever and overly technical ways, but it's just not worth it for these one-off jobs. Keep it simple.