Week 15 fantasy football help?

Week 15's looking really iffy for my team, but I've got faith I can pull through. This is a standard league (8-team).

Here's my roster:

QB: Kirk Cousins @ Atl (Picked him up; dropped Josh McCown after Jay Cutler was named starter)

RB: Eddie Lacy @ Dal (Probable, but a bit worried about the ankle.. great match-up though)

RB: Shane Vereen @ Mia (With Gronkowski on the IR, Vereen's a must-start, especially against Mia)

WR: Vincent Jackson vs. SF (Probable - SF a good defense but Jackson's a must-start, right?)

WR: Antonio Brown vs. Cin (Beat Joe Haden and Brent Grimes.. definitely starting against Cin)

TE: Vernon Davis @ TB (Had Gronk; Davis is never a bad replacement. Go-to guy for Kaepernick)

Flex: ?

D/ST: Chiefs @ Oak (Smacked around Wsh defense last week - should somewhat repeat)

K: Mason Crosby @ Dal

BN: RB Chris Johnson @ Ari (Terrible match-up, but Johnson's been great for the season's 2nd half)

BN: WR Da'Rick Rogers vs. Hou (Lit it up last week, but Houston is a top-10 pass defense..)

BN: RB Rashad Jennings vs. KC (Cleared to play, but KC limited A. Morris to 31 yards running)

BN: RB Bobby Rainey vs. SF (SF limited Marshawn Lynch to 3.6 YPC on 20 carries last week)

BN: QB Aaron Rodgers* @ Dal (Too bad he's sitting again.. friggin' great match-up)

BN: RB Le'Veon Bell vs. Cin (Not liking the Cincinnati run defense - Bell carries for little YPC)

BN: WR Roddy White vs. Wsh (Good match-up but don't like White's inconsistency)

BN: RB James Starks @ Dal (Picked him up in case Lacy wasn't able to play - expendable now)

My questions for you kind folks are; 1) Who should I play at flex? Johnson, Rogers, Jennings, Rainey, Bell, or White? 2) Should I pick up a different QB instead of Kirk Cousins? The best available ones are Alex Smith, Ryan Tannehill, and Mike Glennon. 3) Am I playing the right people? I have a lot of RB options, but are Lacy and Vereen the two best options?

Thanks for your answers, and I'd be happy to answer your questions as well. Good luck in the playoffs, folks.