In my experience, it's much easier to carry heavy furniture and such when your arms are slack and there's nothing in the way of your knees. Generally this means grabbing stuff from the bottom. The weight is supported by your shoulders and torso rather than your biceps.
With that in mind, I think these handles would be very useful for maneuvering the tank into position, but a lot less useful for carrying it long distances. I think the dolly is an excellent idea though, and if you can get one that lifts that's just a bonus. It'll allow you to go as slowly and carefully as you want to without any risk of someone tripping, losing their grip, etc and dropping the tank.
For what it's worth, I bet those suction cups are rated for 500 lbs in shear, 'cause that's the orientation in which glass installers use them.