Contracting would be a very good career track, IMO. And the fact that you're at Columbia is a real clear sign you did your homework when looking for a solid foundation and education in "meat&potatoes" pro audio.
Although I barely get involved in it, the home entertainment market is holding steady as far as what I can see. It may still be booming. It certainly will remain a viable market for a long, long time. But it needs improvement in at least a few ways. One is in measurement and optimization of the ldspkrs, which is overlooked or under-appreciated by 90% of the designers and installers. As are acoustics.
Union ? The larger cities require union membership (or permission) on commercial projects.....anywhere they have a strong presence with certain trades (electrical, theater). But for sound contracting in general, you not only may not need membership...... you may find it difficult to get into a union without working as an apprentice and not necessarily in sound contracting.
Pro Sound News, Systems Contractor News, ProAV, Sound & Communications and Sound & Video Contractor all come to mind as having classifieds for positions in contracting. You can subscribe on line and get free subscriptions to each and all.
As Doug Jones would tell you: sign up for SynAudCon membership and get on the listserv. Lots of contractors hang there.