Answer A.) Just head to the junkyard and buy a broken down car for cheap. If you scratch it or make mistakes, it’s no big deal.
Answer B.) The back windows of SUVs are typically some of the easiest areas to tint. If you wanted to give it a try, I’d recommend starting with this. Trucks are also typically quite easy compared to other cars.
Answer C.) The Volkswagen Golf and the Mazda 3 are both considered relatively “easy” cars to tint. These cars might be a good way to ease your way into the trade.