What I usually recommend to folks is to sign up for the school that will give you the most coverage (i.e. the school whose essay questions cover the most ground so that you can adapt it to other schools). I don't think you need or should sign up with a consultant for every single school you apply to - you should be looking at consultants as a valuable resource, and not a crutch. To be honest, those who want to sign up for like 5-6 schools scare me a bit because it infers a co-dependency thing, like I am supposed to be a surrogate for their application. I usually recommend folks to sign up 1 school (2 schools at most) at a time; most will feel they only need 1-2 schools (sometimes 3), but no more than that - and if they do need more, it really is only for an essay here or there on an hourly basis.
Any consultant who tries to sell you on a bunch of schools or huge bundled packages upfront are, well, shall we say, more like "sales" organizations than client-oriented businesses. Some folks are more focused on the business of selling for sales' sake, while others are in the business of giving advice and counsel. It's a subtle but hugely important difference, and one that I would hope many applicants can distinguish using their own judgment.
Of the schools, you listed, I'd say that Kellogg typically provides the most coverage since they ask a wide variety of questions (and you can probably cover virtually all consortium essay questions as adaptations of the Kellogg essays). Yes, it's not always "cut and paste" but it's not like you have to write completely brand new from the ground up essays either for each school with a similar essay questions. Your career goals are your career goals - what and why you chose those goals aren't really going to change from one school to the next (with some exceptions, but they don't often come up with most applicants).
Wharton has changed up their essays questions completely last year. They may do so again this year. It's a school whose admissions process is in a state of transition and flux (read: they're reorienting the school, and they're still trying to figure out what that means for the admissions process - which is why so many folks have been waitlisted this year - they know what they want in theory, but when faced with actual applicants, they are unsure how to translate what they want in an applicant in theory into an actual admissions decision). So hard to say with Wharton until the essays come out. Traditionally, Wharton's essays like Kellogg's were the most adaptable because they asked a broad range of pretty straightforward questions that many other schools ask in some shape or form.
Booth has a reputation for asking very odd questions, although I think that is changing. In years' past, they've asked questions like "if you were to choose a school mascot, what would it be?" and other unintentionally comical questions like that (no wonder they attracted some real weirdos a while ago..). Their questions are beginning to be a bit more straightforward, and even their powerpoint slide is really just another way of asking "tell me a bit about yourself" without having to limit yourself to essay prose (but at the same time they're not expecting something completely wacky either).