Yokio
1.) Screw two Tamiya ball cups on to the two hole on the left side of your chassis where the battery holder for the stick cells are. Use the stockd countersunk screws. No more battery flying out in a crash.
2.) All you have to buy is the spur and pinion. I know a 72 tooth or smaller spur would fit or maybe a 74 tooth at the biggest.
3.) Just use a long body clip and mount the transponder between the two front body posts on top of the bumper. Or you could buy the associated lexan body mount and attach it to your servo via double sided tape.