Building a wireless keyboard (preferably with a kit)
First, I'd say dump the wireless requirement, at least for the early prototypes. Once you have a prototype that works, and you've picked up some electrical knowledge along the way, you can add-in wireless after-the-fact. Assuming you've designed the firmware well, it should be fairly easiy.

Then, I would say the approach I would recommend would be to target a microcontroller that can easily emulate a HID device. 

The cheap and easy approach, and the one I would take, is to buy an arduino leonardo. The leonardo (and the makey makey, for that matter), both use an ATmega32U4, which is a microcontroller with an integrated USB interface.

Since the USB interface is part of the microcontroller, rather then a separate, purpose-specific device, it can be configured to act as a arbitrary HID (human interface device). In fact, there already exists a library for using a ATmega32U4 as a USB keyboard. 

Now, lastly, you are basically almost certainly going to have to use a switch-matrix of some sort. Aside from designing your own circuit-board, with an enormous IC (such as a 144 pin TQFP, or similar), you are not going to have enough IO lines to have a dedicated input for every key.
This is fine. Switch matrices are a well-understood practice, and if you're really concerned about button aliasing, you can add a diode for every switch, and make the circuit-board incapable of aliasing. 



For the moment, I would suggest you buy an arduino leonardo, and throw together a prototype. I think you're underestimating the mechanical complexity of this build significantly, and having the electronics you need to at least get the system talking to the computer, and acting as a keyboard will let you start poking around at the mechanics.