I think he'll get around 50-80 total yards, but you're really counting on a score more than seeing big yardage from this guy.
First off, great post. But this sentence stuck out at me because I think it's vital. The Texans are a passing team and it's possible (if not probable) that most and maybe even all of their TDs come via the pass. So in order for Foster to really hit the upside many (myself included) think he has, he's going to have to score because if all three RBs are in the mix (and we should expect that to occur) the yardage could be good but not great for him. So can he get a TD? I think that may be the biggest question because we don't know if he'll even be the goal-line guy.
I'm still in the middle of researching Foster but here's what I see from the stats and game logs. Yes, the Texans are a passing team but it's important to ask why. There are reasons for this besides the fact that the Texans were horrible at running the ball this year. For one, there were only three favorable matchups for their running game this year against the Raiders (30th), Cardinals (27th), and Buffalo (32th). The remaining 10 were with run defenses in the top half of the league. Of those three games, only one was an early blow out, the Raiders game. Let's take a look at the stats for that game:TexansRan the ball 41 timesPassed the ball 22 timesOf course, even against the third worst run D they managed to average 2.9 per carry. It is worthy to note that they had their longest rushing TD for 32 yards (only rushing TD over 11 yards) this game as well.Now let's look at the Bills game. The Bills are ranked 5th against the pass and it showed that game as Houston was unable to get going and were only able to take the lead in the fourth quarter. During the first three quarters while the Texans were down, they passed 31 times and ran 18. In the fourth quarter, after they took the lead they ran the ball 12 times (3 for scores) and passed 3. Finally, let's look at the Cardinals game. TexansPassed the ball 50 timesRan the ball 21 timesEven though Arizona is the 6th worst team against the run, they couldn't run because they were down 21 points by halftime. Now, St. Louis is worse against the run and I don't think they can even come close to Arizona in terms of offensive firepower. If anything, this game should resemble the Raiders game the most. The Texans should get the lead early and run the ball against an inferior run D despite being bad at running the ball. A scenario they really haven't had much of this past year. I haven't looked into it as much, but they had to pass the ball a lot in the other games because teams kept putting up points against the Houston D and there were very competitive division matches hence, throwing the ball more than running it. The Texans RBs should get a lot of carries against St. Louis and I think in that respect, the FBG projections are too conservative. However, I think the avg yards you can expect is definitely limited so I don't think you can say 15-20 carries = automatic 100 yard games. They couldn't really take advantage of the Raiders earlier this year (2.9 ypc) and against the Bills, the worst run D by far, they averaged 4.4 ypc. I'll say it again, I think Foster's big day would have to rely on TDs. Not long TDs because Houston only has 3 runs over 20 yards and St. Louis only allowed 11 runs over 20 yards compared to the Buccaneers and Bills who allowed 19 and 17 respectively, but TDs inside the 10. Texans are an average team when it comes to scoring rushing TDs but they get a lot of opportunity because Schaub and Johnson can move the chains. Without a great WR2 or TE like OD it leaves the door open for the RBs to score in the short yardage situations and I believe in the last 10 games, a RB has scored at least once whereas they didn't for the first three games of the year. I'm thinking ODs TDs were distributed amongst the RBs. As for Arian Foster being the guy to get the TDs, I'm not saying he's the new goalline back. Any of the RBs can score, it seems a lot like New Orleans. What I am saying is that he has the build, can catch balls, and they want to see what they have so why not give him at least a couple chances since Brown hasn't been that effective and this isn't going to be a competitive game. They gave everyone else a shot, right? And I'll take a couple chances at a St. Louis defense that allowed 19 scores on the ground/18 through the air over a full time goalline back with a neutral or tough matchup. If he doesn't score, you still have a cushion because he should get the garbage time carries and 15 carries + reception yards against St. Louis for 50-80 yards is a pretty decent number considering the circumstances.I still got to look into more stuff though, like Forte and Forsett vs the Rams to tweak my predictions but first thought is that Forte had over 20 carries and averaged less than 4 yards per carry while Forsett had 22 and Foster might not see as much since he's in a committee. Second thought is that if Forte and Forsett can score 3 TDs against the Rams with O-lines that are just as bad then it's an even better bet than Houston will to

h and I am also looking into Jennings and probably going to look into gather a little too but right now, Foster > Jennings and Gather.