I like almost all of what you mention except fire sales, which disrupt competitive balance.
One thing that I like a lot is a playoff system that offers those teams not in the playoffs to play for the number 1 overall pick in next year's draft. I think such a system encourages continued competition and stretches the season for everyone. After all, fantasy football is fun and the longer a commish can make it fun, fair, and competitive for everyone, the better.
As for trading deadlines, I think they're okay. But I've never seen much use for them when a playoff system like the one described above is in place.
"Happy life day!"