Get a 16k, the Simple & Sinister book, and some personal instruction if you can swing it. The book will answer most of your questions.
Hasbro has given you some good advice. I see you have a number of threads about swings and what size kettlebell to use. You haven't provided any other info. Male or female, size, age, rough physical condition, past strength training info, etc. All answers are a shot in the dark with nothing to go on.
If you're new to kettlebells, male, 30+ years, not much history with strength training of any kind, then Hasbro hit the nail on the head with the 16kg. Forget what anybody else is using. Start reasonable, get some instruction and learn the core movements. Later, when you're ready buy the 24kg. If kettlebells and strength training is new to you, then you can get a lot of mileage out of a 16kg. S&S is a good program. So is the original ETK. Learn the swing - two and one arm, the snatch, the goblet squat, the press, the TGU, the bottom-up press. I'm willing to bet a 16kg will keep you occupied for a while. When you can snatch the 16kg for reps, and bottom-up press it for reps, you'll be ready for the 24kg.
When I started, I ran the ETK program with the 16kg and it was a good choice for me at that time. I can swing much heavier bells now but I put in my time with the 16kg, then the 24kg.