"Also how feasible is it to create the basic shape of a prop in Hammer using Propper, then import it to blender to add in details? "
Very feasible, I did this with blender several times while working on ctf_urbanbrook.
The 3D programs I have experience in are blender, maya, and the adorable wings3D.
Maya 2016 is a buggy, bloated, crash ridden mess and would not touch it with a 10 foot pole if I could avoid it. From what I understand alot of companies that use "Maya" are running a version from 10 years ago that has been overhauled by their own internal teams. The changes autodesk has made to maya in the past few years are depressing.
Blender has improved greatly in the past 2 years and I would happily recommend it to anyone wanting to get into 3D modelling. Although exporting a model from blender to source requires an (easy to get) plugin and a few external programs, but this isn't really a fault of blender and more a fault of source.
Wings3D can't do much but its to darn cute to ignore.