You can pretty much any body onto anything if you work at it. The Overland bodies do have different clips to attach the bodies.
The PN motors are faster. But you will need to motify the board so that the stock FET do not burn up. the safer way to get speed is just put a turbo kit in it and the you can put other motors in it. The X-SPEED is fast enough.
Leave the servo alone~! The only thing you have to worry about the serco is the Pot going out. That's theonly thing you might have to change in the future. If you try to make the steering faster, you'll have to end up buying another RTR in the end.
All Overlands have the same chassis. The hop-up clear chassis(from what I heard)does not flex as much.
Mini-Z's do not perform well on rugs. Ozite, yes and outdoors, it's a bit bumpy but pretty fun. Overland is just plan fun everywhere~!
There are many hop ups for the Overland from Kyosho, GPM, Square. My Overland I only use Kyosho hop-ups. Save money and buy Kyosho hop-ups. Bearings are the first and then shocks.
I raced and played with my Mini-Z and Overland in Hong Kong many time. Really fun on the tracks with jumps and hill climbing~! Most of the guys there recomend just using only the X-SPEED and nother more(they burnt out to many boards)and using some Kyosho hop-ups.