Speaking as a breeder, if only very occasionally, I would way rather have the essay than something really short. Politely formatted, as suggested, with the important points in paragraphs of their own. I'd put the most important stuff in the first few paragraphs, and then all the other detail you want to include, questions you want to ask, etc.
This will give the breeder a better "feel" for you, and if you are someone they are interested in selling a puppy to. Others may feel differently, but I think if someone was a breeder I wanted to buy from, they'd be interested in knowing as much about the buyers as possible, and a long winded email in the buyer's own words will tell them much more than answering questions will.
ie; if I ask someone "did you have any interest in competing in sports with your puppy, or is this intended as just a pet?", they might answer that they are interested in competing in agility, because asking the question led them to think I expected it. This could lead to them having the wrong puppy if they weren't really that interested in agility. Whereas if someone writes me a rambling email about their experiences with dogs, and their hopes for their new puppy, and brings up their interest in competing in dog sports, it's a pretty safe bet that they do intend to give that a try. And of course, the parts about their previous experiences will give me some idea of what they are used to from a dog, and what they are likely to be able to handle.