1. NF editors are looking around at a lot of magazines and online sites for good work. A lot of them look at unagented work too.
2. Platform is critical but if you don't have it and you write really really well, they will help you find someone with credentials to write a foreword, or sign on as a co-author.
3. The weakest things in most proposals is the competitive books section.
4. The second weakest thing is the lack of specificity about platform. If you have a speaking career, they want to know how often, and to what specific companies, and for how long you've been doing it.
5. Word count isn't a big issue here, but generally you'll want a book that finishes between 200-300 pages. Assuming 1.25 manuscript pages per finished page, and 250 words per manuscript page that's somewhere between 250-375 manuscript pages or 62,500-93,750 words. Remember though..word count isn't a huge factor.