Whew that was a hard block to read
@Shadowmeph but I think I got it
Core work has actually been debated in the literature; some specialists saying it is good, some saying it can do more damage to the low back by putting too much pressure on the injured area. The specialist I was seeing several years back basically said what I said above: carefully do core work and see if you find it a benefit. If pain is greater than benefit, then don't focus on core stuff.
My personal experience was doing only a small amount of core work when things were bad, and then slowly building up as I improved and had less pain. For me keeping the weight down and doing some core, say 40 crunches and 40 leg raises a day, keeps things tight enough to give my back support but isn't too much to strain anything. I'm no Ironman but even that little bit it helps!
That's what has helped me anyway, once I was out of acute phase. And other general exercise, time on the elliptical, some weights, and stretching all to keep mobility going.