If you are just starting out you will be fine just getting the 16kg kettlebell. Do your research (particularly about Pavel Tsatsouline) and you'll find more exercises than you need. If you're average or slightly above average strength you may also want to get the 24kg or one a 20kg bell. These would be used for things such as heavy swings. You should hold off on anything heavier until you can strictly overhead press the 24kg for about 10 reps per arm.
You can't go wrong with the Rite of Passage program from "Enter the Kettlebell". Its simple, effective, and can be tailored to suit your interests.