"Not sure how this is a plan for failure. Blanket statements like that without anything to back them up are useless on forums like this. I also don't understand how the first part of your post has anything to do with the approach professionals take towards purchasing gear. The first part has to do with what type of photography we will be doing. The second part has to do with pros think it is better to start with smaller, cheaper gear and build up, or spend a lot more money right off the bat to get the best gear available."
Well, ok. "Newborn to wedding to sports". How do you plan to be an instant expert in every variety of photography genre to be able to fully satisfy your clients? By "newborn", I assume you mean in studio portraits. Do you have plans to purchase posing tables, fabric, backgrounds and setup an online proofing gallery for parents to look at? Simple shots of a newborn in a studio does not require a camera with a high frame rate shooting ability.
Weddings - Are you instantly well versed in producing trendy albums, you know all the shots that clients expect, do you have a camera that can shoot in low light due to venue restrictions? Do you have proper attire for events, as well as the extended hours to shoot? Small flashes and modifiers that allow you to move about the reception, getting good exposure while keeping the ambient high, or are you going to look like Uncle Joe with his P&S?
Sports? Do you have a camera with a high FPS, like a 1dsMk3? A wide range of autofocus points to be able to lock on to the action? An account at a printer offering all those keychain and calendar things? Or are you planning portraits, and you have 4 shooters, with duplicate cameras, lighting setups, and a system for tracking what team and individual you are shooting?
See? You can't really just walk into Photography, and say "I'm going to shoot everything. What's the best camera to buy?". You will try to satisfy everyone and end up making no one happy, because you don't have the experience, or connections, or equipment or knowledge. Best to concentrate on one thing first, master it, and then spread out.
With a business plan, you would know what market you are concentrating on, what the planned return would be for that market, and what equipment you should purchase to meet the needs and return for that market. ie., for portraits, you don't need an $8000 1dsMk3.
See?