The G1000/GFC700 is a BIG step up from the KAP140. You now have Vertical Navigation capabilities (in descent at the moment, possibly climbs in the future), airways in the flight plans, several new pitch autopilot modes, and a difference in how the nav system sequences through flight plans.
There's a reason the guide for the system is 400+ pages, it does quite a lot. You can of course fly it and not use many of it's abilities, people have done that for years in airplanes with GPS and autopilots. You'll be selling yourself short, though.
Garmin offers simulators for the various airframes. They're less than $30.00 and well worth it. Get the sim, download the book, fly a few "trips" and learn the system, then go up and get some dual. Be sure to focus on abnormals in the dual - instructors now have some overlays that fit on the G1000 to simulate failures, and they make a big difference in realistic training.