Having your elbows flared back is bad form. The elbows should be pointing down to the ground; your forearm should be perpendicular to the ground. The reason is you are keeping your upper back very tight. By pulling the elbows forward and flexing your upper back you are creating a very stable "shelf" for the bar to sit on. You also have to find the "notch" between your medial and posterior delt for the bar to sit in.
In theory, doing abs before heavy squats would weaken your abs and not let you squat as much as you could. I would not recommend doing abs before a max attempt at a powerlifting competition.
In training, it is wise to do abs to build work capacity before your working sets if they are your lagging muscle group. 3 sets of 8 reps is enough. This will get you started in the right direction. Then after your squats hit the abs harder with some other sets.
Even better would be to do abs on a separate day if they are your lagging muscle group. Doing abs hard before your work sets can be done infrequently to test your abs. If you fail on your work sets miserably = low work capacity in abs.
Low work capacity will hold you back from working out harder. It takes more work capacity to bang out 5 sets of 5 with 495 than 5 sets of 5 with 315.
Hamstrings is another muscle group that usually hold people back from hitting big weights, but that is another story.