The 12.5 kgs is a lot quicker and will be strong enough. My Ace DS1015 that I use is the same and is plenty for my Hyper. You really need the steering speed when racing.

Unfortunately, I do not have any video of my car, but if you search on youtube, you should find loads of videos showing racing engines in the car. I woudl stick with a good race 21 instead of a 28, purely for the runtime. Nowadays a good race 21 is not that much slower than a good race 28 if at all. I have beaten guys who have been racing longer than me with my RB WS7 III while they were running OS 28's and the like.

As for the radio tray, unfortunately, we are stuck with what we have, or you could try one of the radio trays that other guys have used, including the Kyosho and the Hyper 8.5 box.