Trailers are generally cut while the movie is still in post. If the director has a choice between working on the movie or working on the trailers, he'll pick the movie, as well he should. I know a guy who writes trailers for a living. He makes about $250k a year.
Depends. WGA schedule of minimums Take 10% of that for the agent, 15% of that for the attorney and 20% of that for the manager. Then know that sometimes you get better than the minimum. Bill Marsillii and Terry Rossio sold the script for DEJA VU for 8 million.
SELL a script a month. Nobody does that. The statistic that is bandied about but isn't well attributed is that there are more players in the NBA than there are screenwriters in the WGA who are actually making a living writing screenplays. I've optioned two, which puts me ahead of 99.99% of everyone who's ever tried.