get the losi hd diff cases. The gears hold up fine.
If you can do without reverse, get the foward only conversion. This will cut the weight and make for less moving parts in the tranny. There is also a way to swap two of the gears around to get more top end speed.
As far as motors, the lrp 30 is a good choice. Nova 528 is an absolute beast.
Wing kit is good for stopping wheelies. Does not do much for down force.