No experience with the 24-105, I'm afraid. You can check the internal dimensions on LowePro's website and compare it to your setup.
The 5DII and 17-40 fit the 70AW with 1" or so of depth to spare... if my recollection is correct. The TopLoad Zoom 2 is a bit more snug, so it might be a bit too tight with a 24-105. A 70-200 f/4L IS does NOT fit in either, if that gives you a better reference point. I'm sure a 75AW would work -- but now you're adding more bulk and a wee bit more weight.
Nope, just 2 'biners makes a secure connection of the bag between your shoulder strap (low, down near where it ties into the bottom side of your pack) and the hip belt.
Think of the bag sort of hanging from the two 'biners, but there's a enough tension that it's pulled in snug against your hip belt about halfway between you bellybutton and hip bone.
If you had a bag with a D-ring on two sides of the body, just below the lid (like the LowePro bags), it would become immediately obvious how you'd attach it. I'm sorry I don't have a picture... and it is sort of odd to try and describe it in words. 
Gary