Barnes, Casspi, Tolliver, and Gay will all see time together at the 3/4 spots, you can bet on it. And I would argue they SHOULD to give Boogie space to work in the post as needed.
Over the past 2 years, a lineup of Collison/McLemore/Gay/Casspi/Cousins has been outstanding (even just Collison/Gay/Casspi/Cousins with the 5th player not being another PG). That lineup has produced an offensive rating of 119.8 and a defensive rating of 98.6 which is a 21.2 net rating. The Spurs led the league last year with a 11.8 net rating as a comparison.
I discussed this lineup in the other thread and opted to keep Cauley-Stein as the starter for more defense and to give our bench some much needed scoring punch, but with Lawson on the team, I think I'm leaning towards swapping Casspi for Cauley-Stein if Afflalo comes off the bench. Lawson & Afflalo coming off the bench would hide their weak defense and give us some bench scoring options to help balance out the team. I'd be looking at McLemore (if he's made strides this offseason and has EARNED the starting role) or Temple as the starter. Temple's presence gives us another above average defender in the lineup who knocks down C&S 3s at a similar efficiency as McLemore did in the Collison/McLemore/Gay/Casspi/Cousins lineup. It also gives you a guy who could effectively switch 1-3 and even switch onto some smaller 4s considering he has a 7'1" wingspan.
If we moved Koufos for a pick & TPE, our rotation would be pretty balanced and we'd play a fair amount of smallball.
PG - Collison (30 min) / Lawson (18 min) / Farmar
SG - Temple (22 min) / Afflalo (26 min) / McLemore / Richardson
SF - Gay (34 min) / Casspi (8 min) / Barnes (6 min)
PF - Casspi (20 min) / Cauley-Stein (14 min) / Barnes (14 min) / Tolliver / Labissiere
C - Cousins (36 min) / Cauley-Stein (12 min) / Papagiannis
Cousins - 36 min
Gay - 34 min
Collison - 30 min
Casspi - 28 min
Afflalo - 26 min
Cauley-Stein - 26 min
Temple (or McLemore) - 22 min
Barnes (or Tolliver) - 20 min
Lawson - 18 min
McLemore could replace Temple in the rotation if he's looking like the 3&D player we've been hoping for and you can alternate or mix & match Barnes' 20 MPG with Tolliver depending on matchups, hot hand, etc.