Is it possible to carry out vector editing functions in QGIS? In this case I have an imported shapefile of contour lines. I wish to be able to create a copy of a line, in-situ, trim it, then create a number of offsets at a specific spacing. In short, basic CAD tasks.
You can install QAD plugin which does exactly what you want. It has trimming, extending, and other interesting tool like simple CAD, as you can see below:
This is the only tutorial I found of QAD Plugin, but unfortunately it is not in English. But I think you can still follow because the commands are in English.
The Advanced Digitizing Panel has tools that will be of use for you. I use it to start a predefined point, move at a specified distance and angle to my point of beginning then begin digitizing from there specifying line lengths and angles. Here's a video tutorial for more information on the panel and the related trace tool:
These tools became part of the standard installation as of QGIS 2.8.