I would but and test sensors by setting the controller there with a single led. Then as you walk around watch to see what combination works the way tou want it to. Once you get the control sensor right, then build the rest.
Just a thought, if you have a metal handrail on the stairs you could use that a a touch sensor.
That said the easiest thing they can do is just get a LED Strip that is able to be added directly into HA via zwave or zigbee and use the circadian lighting integration to automatically control the brightness and temperature of the strip to keep it a more natural light at night and use say an aeotec motion sensor where its best for detection of a person on the stairs.
this is his blog about that…but he did not share the code…I guess doing that with home assistant is better …it is the same idea of Arduino but in home assistant