Besides one being black it appears (according to their specs) that the black tube is a bit tougher.
I was never big on having a res. Personally, I would always have a T line but I could never get them to work right so my vote goes for the smaller res.
That heatsink isn't necessary.
Grain of rice, always. People tend to forget exactly what TIM is for. You don't need a perfect layer as that can just cause heat blanket effect, as can the air bubbles. The pressure between the metal surfaces spreads the paste to fill the microscopic dents between the metal for perfect contact. Spreading yourself can cause air bubbles to form between the IHS and paste which will cause your CPU (or GPU) to be warmer.