How to create geometry with "point and click" and set number of vertices? I am trying to devise a way where I can "point and click" to create a line geometry and specify the number of vertices in this line.

So, this would look like me setting a "start" point / vertex by clicking, and then clicking at some other location to finish the shape (forming a line) but then being able to specify the number of vertices in that line (equally spaced) so that I do not have to go through the long process of extruding and dragging each time I want to create a vertex or trying to subdivide after I have made a line.

This way I could just click two points in 3D and say "join these points with a line that has X vertices".  

Is there a pre-existing or relatively straightforward way to do this? The reason I am interested in using a "line" is that I am trying to make a correspondence between each vertex and a light, so I do not need a grid which would have two vertices at each point.
This is a rather trivial problem. In edit mode, in the 3D viewport, locate the 3D cursor where you want the first vertex (starting point) and while holding down the CTRL key, click the left mouse button. Then, move the cursor to the location at which you want the other vertex (end point), hold down the CTRL key, while clicking the left mouse button again. Now, select the first vertex, and while holding the SHFTkey, click the vertex that you chose as the start point, and press the Fkey to join the two vertices with a line segment. With the line segment selected, use the subdivide tool (press the spacebar, and enter "subdivide" in the search bar) to create the number of intermediate vertices desired. The default behavior of the subdivide tool us to space the intervenient vertices equally between the end points.