My wife wanted something the kids could do, too. So they painted the risers. We also clear coated them (using whatever the local paint store recommended). And we used the same clear coat for the design on the landing.
For the railing, I have these cheap sawhorses:https://www.homedepot.com/p/Stanley-22-in-Folding-Sawhorse-2-Pack-STST60952/203768844
Those grooves are for 2x4s. We had brass hardware for the railings originally. I had some 2x4s and I attached the brass hardware to the sides of the 2x4s. I put plastic sheeting around and over the sawhorses, then put the railings into the slots. This allowed me to paint the railings while attached to the 2x4s. I put the railings so they stuck up above top of the 2x4s, so I could paint all sides. The only detriment was I could not paint the bottom easily, but you don't see that anyway.
I sanded the railings with multiple grits of sand paper, then primed them with several coats of primer. I let that dry then lightly sanded that and then added the silvery top coat (multiple ones).
At that point, we had a storm come through and lost power for 8 days. We lived on a generator.
When the power finally came back on, I added the clear coat. I forgot to lightly sand the top coat before the clear coat.
We also replaced the hardware with the brushed nickle.
As for painting the stairwell, my wife did that and said it sucked. I could see that, as it's difficult to paint while standing on the steps. The ceiling and top parts of the walls were tough.