Really, I'd just reiterate what everyone else has said already. You can always modify the kits later down the line too, after you get a bit more clued up on what everything does - I wouldn't suggest a complete overhaul, but you've always got that option and failing that the stock machine's a solid choice anyway for a beginner to the sport.

Generally speaking, your basic parts don't tend to change much as you progress through the weight categories from what I'm aware (though some ant/beetleweights use servos to drive instead of a speed controller/motor combination) so once you learn the basic layouts you'll be able to build something from scratch if you'd rather go that route as well.