Hi Norteno! To answer your newel post question: this is a "post-to-post" type rail system as opposed to an "over-the-top" system. Post-to-post has a squared flat spot on the sides and the rail dies into the flat spot. The one shown in this picture is an end rail since the flat spots are not very tall. An intermediate post will have a tall flat squared area near the top and rails will enter / exit the post at different elevations and sides. These would be found at a 90 degree turn landing or other locations.

An over-the-top system has a newel post that has a cylindrical pin at top that is subsequently hidden. The pin is about an inch diameter and fits into a hole in the bottom of the rail system that sits atop the posts; hence the over-the-top designation. These systems are generally a little more expensive and at the bottom of the stairs a "volute" or "turn-out" may be installed.

Secondly: the post Is 3 1/2" square and was roughly 60" tall before we custom fit it down to about 42". Your stair system and the placement of the post will determine the length of the post. These posts are intended to be cut at the bottom and usually are not even cut square from the moulding shop. You are welcome to call us for details if you wish.