I liked your lab setup. I videoed my projectile lab, but I used a photogate timer to time the ball and find the speed of the ball. I also used hot wheels tracks for my ramp.
Yes, but not by an appreciable amount. Rolling friction is very different from sliding friction. And at such low speeds, air resistance is negligibly small as well.
Not significantly. In an absurdly perfect test we might even be measuring the distance the earth rotated and travelled in it's orbit around the Sun in the time the ball rolled that distance. But it would not change the results we can measure in this test.
