Ok, you answered exactly the way I thought you would - it was sort of a loaded question, now for the second part of my reply -- The King Air 200 is a great airplane, I'm a big supporter of the King Air line, and you named all the right reasons to buy one but you missed the important criteria! Don't let yourself fall into the trap of buying the perfect airplane for YOU - make sure to get the one that is going to be the perfect airplane for your OWNERS!! That's critical. A fractional operation is going to have a very limited (relatively speaking) market - you can't rely on the "Buy it and they will come" strategy. Make sure you do sufficeint research among your target/potential customers and see what they NEED before you decide on a particular model of aircraft. Granted, the BE200 is one of the best 'all around' airplanes there is but let's face it - if the client needs a 350 then he's not going to be happy in a 200 and won't be a client for long. Likewise, even though you don't consider the BE90 to be a good choice, if the majority of your potential clients take 1 or 2 people on day trips of 150NM then you'd be doing yourself and your client a disservice by spending the additional money on a 200 when you don't really need one. It's all about client wants and/or needs - just make sure you do sufficient market studies first.
Also, I'm sure that you've already thought of this, but start making a list of charter companies that are close to you that fly the same model of aircraft - or something very similar - that whatever you end up choosing. Unless you're going into it with a 'flying club' type mentality where the scheduling is first come, first served you're bound to run into those days where all of the owners want to fly at the same time so you're going to have to have a way of providing that supplimental lift capability. Even with NetJets extensive fleet, they spend a gazillion dollars a year on charter aircraft to meet owner demand. Also, in the contract with the owner, make sure you promise them it will be THEIR aircraft that picks them up.
Good luck - sounds like an interesting project!!