For all this to happen, I assume you're living in or around a larger metropolitian area. Flight instructing part is probably the easiest to get, seeing how there seems to be an abundance of these jobs, but for how long, I don't know.
As far as the 135 side, this is sticky. Contacts/connections with someone if you're low time, and low-time for me as far as a commercial pilot position is less than 1000 hrs. There are operators that use 2 pilots in twin-piston planes, mainly C421's, C414's, PA31's, and occasionally the lighter Be58's and C310's. Most likely a lot of these "positions" are going to be very low pay, and you're there for the sake of Insurance, not FAA reasons.
99% of these you will not be legal to log the SIC time, because all of these planes are single-pilot approved, and I'm almost 100% guarantee'd that they have an autopilot, so even 135 they don't need the SIC. You can log any 91 legs assuming you have all endorsements including High-Perf, High-Alt, etc..(421s'/414's require high-alt endorsement).
So "realistically" speaking, looking for these positions as a way to get your foot in the door, is not a bad way to do it, but it's not always the easiest of ways. I do think it offers some real-world experience if you can get into something of this nature because you can see how the pro's do it on a day-to-day basis. It will not be a good source of income in most situations, unless turbine equipement is involved, and also a lower time-building venture as well, but I feel in this case it's "quality" vs. "quantity" of hours that really matter.