Pro Tip 1 to Turn 2 to burn. Steering servo will always be channel 1 (1 and 2 and Traxxas Recivers)> Channel 2 is for the ESC. So the Gyro would also plug into Channel 1, and the servo into the gyro, and if you have the single signal cable, channel 3 and beyond.
Both chassis are pretty decent but I would recommend the YD-2s. Also check your local drift track ad see what people are using that way they can help you with setup and easier to get started. Hope this helps
most drift cars use 13.5 or 10.5 motors. For competition it all depends on the event really but I would stick with the 2 I mentioned as they are the most common.