Try to get all 4 winters if you can. No good having traction if you can't change direction or stop.
Even a good set of used winters is OK (check them over carefully though). You can save some $$ that way.
Weight in the truck (sandbags) does help. Don't go overboard though. Remember, all that weight has to be stopped too. In the past I have put 100-150 lbs in the trunk, as far back as possible. I do the same in my truck, but a little more weight.
Blizzaks have good grip, but seem to wear fast. I have had good success with Pirelli W210P as well. They last longer, and aren't very noisy.