You've got scoring right. The threshold is multiples of five: 1-4 = 1 point, 5-9 = 2 points, 10-14 = 3 points, etc.
Sets are based on the icon of a target. Escape the Vent has the addition frames, which contain targets from different sets, but, like, all the targets with squid icons are in one set. All of the ramps *are* a single set, so to fill them you would need, like, 2 3 4 5 6 7 8 9 10. You'd need a similar spread of numbers to fill the bumpers actually. This is a rough table.
I hope that's useful!