Hi! I want to make a chorded two hand key board. I wonder what parts or set to buy.
I visualize two controllers (one in each hand) each with 5 buttons.
It is essential that the 4 non-thumb buttons on each controller can be monitored for multiple keys being pressed simultaneously thus creating a "4-bit" signal so that each hand can produce 16 different keystrokes by pressing on those keys.
Thanks for any kind of help!
See this topic for a 13-note keyboard. Arrange the buttons however you'd like.
I want to make a keyboard for making characters (letters) replacing the traditional keyboard on a pc. Not a keyboard for making sound. But thanks anyway! 
That's entirely possible. You need to use a Micro/Leo since you want it to act like a USB keyboard, so you need something with native USB.
There are plenty of guides to pretending to be a keyboard (USB HID, it's called, for human interface device) with arduino.
Also - nothing special about using the buttons - because you need to know the states of ALL buttons, you can't use a matrix, so just treat em like basic buttons, as done in countless examples
I would be inclined to use all pins from the same port for those 8 keys you mentioned, so I could read all the 8 finger-keys with one line, ie, btnstatus=PINA (or whatever port you use), which would save you the effort of converting 8 digitalRead()s back into a single value, which I assume you'd end up doing. But maybe that's best left for later - I have no doubt you could make it work without tricks like that.
Thanks for the reply, but I'm still a little confused on what parts to buy.
A Pro Micro.
Arduino Micro (or clone thereof), 10 buttons, and some wire (maybe dupont jumper wire and pin header?)