Hi all, thanks very much for the replies and the help, allow me to catch up.
tallakt : The main purpose of the system is to produce power while remaining somewhat compact, the payload is just an additional accessory which would be fun to have but again is not really our main goal. Our current plans on making the 20 W are to have a reel in and out system, it appears this is called a “yoyo” system as Pierre posted below your comment. The Kitewinder seems really cool, however it also appears to be out of our skill range. Thanks! 
PierreB: Thanks, we have not really considered that a stiff kite would be more difficult to depower than a soft kite. Though, would a soft kite still be able to generate the lift needed to support a payload? If I am thinking right, soft kites do not generate much force.
Kitefreak: We did not at all consider the usefulness of a kite messenger, but now this seems like it would end up being the best option for our goals, thank you very much!
So now I guess the question becomes what kite messenger to use? This parachute kite link you posted Pierre seems interesting however as kitefreak mentions wouldn’t a parachute kite have some issues ascending the line when tilted?
Thanks again all