When it comes to weight ratings, its always better to double up. Remember, that weight rating is at the TOP LIMIT of what your winch can do. Same goes for all other equipment. You don't want to come anywhere near that rating.
As far as the steel vs synthetic debate, its just a matter of personal preference. 5 or 6 shackles should be more than enough. You should have three different straps: 1. tree saver 2. snatch (aka kinetic) strap/rope 3. tow strap/rope/chain. The tow strap and snatch strap are two different tools. The basic difference is the snatch strap will stretch while the tow ropes/straps will not. Make sure you know which is which.
When it comes to chain, you don't need much. Probably not more than a 10' length. You should be very careful how you use it. DO NOT YANK on it. Pull nice and easy if you use it.
Line dampers can be all kinds of things. Basically it can be anything that can be lightly wrapped around the line with a weight so that if the line should break, it won't go whipping all over the place. I personally like to use the afore mentioned bridles by wrapping it one full time around the cable and weighting it down with a shackle.
I prefer to use a snatch block whenever time allows. It doubles the pulling power of the winch while halving the tension on the cables. You're basically doubling the cable used to pull so its MUCH safer. It does take longer, since the winch has to pull in twice as much cable, but when it comes to winching, slower is almost always better. And if you're that pressed for time, you should either A: grab the snatch strap, or B: evacuate and return at a time when you're not having to race the clock.
On the knowledge, look around and try to find a copy of FM-22. The army's old Field Manual on emergency vehicle repair/recovery. It has a whole section on winching, including how to make an anchor when no trees are available. Hard copies are rare, but you can purchase a digital copy in a PDF format and read through that, or print it out yourself.