They really need to start with individual films like a wonder woman or Aquaman to start the buildup towards a JLA movie.
Not really, an Aquaman or Flash movie would tank horribly at the box office, and Wonder Woman would be hard as hell to pull off as a solo film.
If they did Green Lantern well it could make money, but I think they would have been off choosing a more gritty Lantern rather than Hal, he just doesn't mesh as well with today's audience. And that's a similar problem Superman has, but Superman is much more entertaining and able to do well if the film is right.
I think if they try and follow the Marvel strategy to the letter they will fail horribly, their original characters are too hit or miss.
They have very cool characters, but they would have to modify their style and go with characters like Green Arrow that are a bit more grey and have more personality.
Hell, the whole Young Justice series on CN is fantastic, I don't see why WB couldn't do something like that for Justice League.