I'll just pile on here. A 20kg might be a great one to start with for you. Check out
Lifeline USA Functional Fitness Equipment 1.800.553.6633 for pretty good KB prices.
Good foundation exercises are swings (one and 2 hand), cleans, snatches and jerks. They excel as a strength-endurance tool and allowed me to remain in outstanding condition in terms of cardio without running (I don't like it). To quantify that statement, I cut my 2 mile run time (for Army PT test) by over a minute in 18 months and I only ran maybe 6 times in that period. Granted, that's not huge, but I wasn't focusing on running at all.
A bigger benefit than the crossover aerobic benefit is the anaerobic benefit. My recovery time has never been better. I gave my soldiers what I would consider a medium workout last month...half a dozen puked...ooops! Most of them are 10 years+ younger than me. It is the National Guard though, most of them don't workout much on their own if any...I'm trying to change that! Enjoy your KB, they're addictive, between my wife and I we have eight now.