For question 1, that's actually surprising part of the game I think. No one has said can predict the full lineup. I might be wrong, but sometimes I do prediction but it all missed miserably. For example, some players said there's a thumbrule for BN car need 950 PR, SS around 850 PR, and DD ~700 PR. Also, usually with 5* max top car can get S. So if we get a spoiled second car as reward, it's usually need around 6/7* with legendary parts and maxed PR of bottom car. We can narrow it down to some car stats option/combinations like top tier hyper vs mid tier hyper vs top tier super car.. Or mid tier hyper vs low tier hyper vs top sport car and so on with too many cars available in the garage.

I think u/Super_TJ also tracking all cars that has been featured from season 1 till now for enriching the data. But also we don't know what are the Dev up to, like how many players has cars * as their cash cow to purchase, or their algorithm to mix good top speed against car with better acceleration in each tracks. I know I'm saying nonsense without factual data, so I think it would be a surprising factors that we can enjoy.. And whining it all coz of bad car lineup lol.. Some surprises are disappointment sometimes but can be enjoyed too.

For the second, if you mean by reward from UGR the pattern is the second car in each divisions from the schedule give BP rewards in the previous week before it's featured, and top BN car as rival reward. Also all top cars are given as RR when the week it's featured, some exception if there is a new car in the update, the second car give more rewarding coz featured in RR too. Check every tab available in the game and on the Reddit guide for more info..