bluesideup,
You'll discover there is as much variety in pay and working conditions among various 135 operators as there are among different 121 airlines.
I can't speak to your concerns as I have never flown part 121, but I can talk a little bit about what you'll expect.
The pilot/dispatch relationship of shared responsibility is gone. The dispatchers you'll be working with now (for the most part) think that second segment climb is what you'll be doing after takeoff on the second leg of the trip. As a result, its pretty much your show out there. Comlicating this will be the culture the operator has in regards to their expectations. ("what do you mean it's illegal? the OTHER crew did it!) Hopefully you will ply your trade at an airline where they understand the importance of safety and following the rules. Also complicating this and other issues is......THE CAPTAIN.
Much like the 121 world you're going to to encounter the whole gamut here. From guys or gals that should have been astronauts and are amazing to work with, to insecure, untalented hacks, whose demeanor sucks all joy and life out of the cockpit. What you'll notice here more than anything is that 135 cockpits (with some notable exceptions) will be less standardized than their 121 counterparts. This makes the latter category of Captain mentioned above much more challenging for you as an FO to deal with. Protect your certificate.
Chances are however, the 135 operator you'll be working for will have a somewhat descent schedule, and the pilots you'll fly with will be average folks. That having been said, the biggest challenge or difference you'll see is that as a 135 on-demand pilot, you wear ALL the hats: Pilot, Dispatcher, Bagage Handler, Flight Attendant, Concierge, Babysitter (pets, kids or other pilot) SOC, Limousine Driver, (when your PAX transportation fails to show) and others. Your days of putting your headset in the bag and walking up the jetway through the terminal to a waiting shuttle are over. Approach these differences with an attitude of: "Cool! something different" and you'll have fun. I spent the other day BS'ing with the CEO of one of the most succesful companies in the U.S. (he served US in the cockpit!) I've had to contend with the SOP dilema of PF/PNF responsibilities concerning topless dancers in the cockpit attempting to show us their um...goods. (My wife actually thought it was funny)
The bottom line is this. Getting paid to fly airplanes is great. Enjoy the new experinces associated with 135 flying. It's all a question of tradeoffs. For instance, I have an 8/4 schedule that's pretty good considering I don't fly every day I'm on. I had 24 overnights in 2002 (not including recurrent) which keeps me at home with the family after almost every flight. The tadeoff? the occassional 0200 to Guatemala City or a two-day tip to nowheresville where th hotel TV is broken.
Enjoy your new job. It will broaden your horizons and perspective.
Best of luck!