Blue Yeti http://www.amazon.co.uk/Blue-Microphones-Bidirectional-Omnidirectional-Microphone/dp/B002VA464S/ref=sr_1_1?ie=UTF8&qid=1381606181&sr=8-1&keywords=blue+yeti
It has been a while since i used this mouse, but typically you create the macro, select the button you want to customise in the main screen, then select the macro on the button.
The cost would be huge, a single switch will cost around $1 if you buy 50, but if you were to replace just the letters, it would be more per switch. There are better keyboards than the K60, the CM Storm Quickfire TK for example, or any Qpad keyboard