[frogvalley]

The commercial staircases are a good way to see how to construct them. I concur on the central pipe theme with larger pipe sections that slip over the column for each tread. These can simply stack if cut from the same length of pipe as the column and then divided into equal sections for the treads. I just drill two holes and thread them 3/8-16 and use allen head set screws to keep them from turning. For the pickets I would use two for each tread( that keeps the math to a minimum and all of them the same size), both of which hang over the edge and attach to the next tread as well, one up from and one hanging down from.Two holes in each down low will allow you to space the treads properly. Using pipe for the hand rail is the simple solution, either weld in place after bending, or drill thread and bolt, or drill over size holes and toggle bolt into it. flat stock is a little harder to get to bend to that shape, but can be done too.

As to support for each tread, it depends on the material that you want as the tread. If metal is the final, then simple angled pieces of plate welded under the tread and to the pipe section can work. If more decorative wood is to be used then construct each tread/step as a frame attached to pipe and then use rod from the outer edge of the tread to the lower edge of each pipe section.

If you have trouble visualizing what I am talking about, I'll get off my lazy butt and make a sketch.LOL