I am replacing on old iron railing that was not up to code with wooden balustrade. The length of the railing is about 100 inches. I was planning on using a half newel against the wall and a 3 inch newel on the open end. For stability should I install a third newel post in the middle of the span? Also, I need to suspend the shoe rail a couple of inches off the floor to accommodate the stair nosing. What is the best way to attach the shoe rail to the newel posts? I've seen some people suggest toe nailing, but is there a better way to get a more secure connection? Thanks.
I wouldn't install a post in the middle if at all possible. In such a short section it could also serve as a hinge point. I've reviewed many achritectural calculations which show that the load compliance work for 8' and some report on 10', even 12' spans. It all depends on how secure you make the newel posts. Traditionally, we've avoided newels in runs 10' or less. The starting newel is at its greatest strength if mounted down into the framing. Otherwise, if flush mounting is the option, a Sure-tite newel fastener would be the best means of attaching (as long as there is backing under the floor).
For suspended shoerails in wood, it doesn't work well to simply toe-nail into the newels. A child can jump on the shoerail and break it out of its attachment. I learned long ago to take an S4S block (we called these "shoe blocks") and attached them to both ends to the newels and one in the center. These are usually in 4/4 or 5/4 in thickness, slightly less wide than the bottom width of the shoerail; and about 2-1/2" or 3" high depending how high we want the shoerail set. The blocks, in your case, would be nailed to the newels on both ends. You can then cut the shoerail tight to fit and set it on the blocks, nailing or screwing to the blocks before installing the fillet. Keep the additional block in the center which just keeps a pressure for the center sagging or breaking own if stepped upon. The blocks are not large and will not draw attention.