Don't overestimate Greene just based on one good game. And don't let the Patriots fool you, either in that game- they're still a poor defensive team. Miami > Patriots in run defense, so Greene isn't that good, I'd say.
Conversely, I think Stephens-Howling is a bit risky, but I think could be a great RB for the flex spot.
As for WR, I'd stay away from Smith (I assume you're talking about Carolina's Steve Smith, haha), because a) Cam Newton isn't doing too well and b) Chicago defense, scary as hell. Maclin is an interesting start for the second flex position, but again is a bit risky. He and DJax pretty much split up receiving, but Falcons D is pretty tight.
But I'd go Bowe over Maclin- even with the risky QB situation, Oakland secondary is atrocious. I wouldn't start Lloyd because you're starting Gronk, and you want to hope for Gronk to dominate and no one else really getting anything... It's a risky mindset, I know, but I feel like that's the way to maximize upside. If you take 2 players on the same team (unless one of them is the kicker or the defense), you're essentially putting a cap on what the most points you can get from each of them is. The flipside, of course, is that you're hedging your bets and getting some insurance that at least ONE of them is going to do SOMETHING, but I myself don't like playing that conservatively... Besides, realistically, what are the chances of the Gronk getting shutdown and not getting anything??