Quick5pnt0:
I think there are a number of things you'll want to ask yourself or plan for before starting the project. First off, what is the point? If you have to hand the customer a code number to get their key out, why not just hand them the keys? How would the keys be placed back in the mechanism afterwards? What would stop somebody from saving the code so they can get them out over and over again for free? What type of "switches" were you thinking would work to hold the keys?It sounds like a feasible project though I'm not sure how you'd control the key holding mechanism? I guess you could use servos but then you'd need to figure how to get more pwm channels.
Codes would be easy to incorporate into the confirmation of reservation email that we send out to guests when they initially contact us. The main purpose for us would be convenience and security for our guests. As a state agency, we don't have the budget to have an "active" employee after hours - but there are 3 of us that live on the park grounds. As it is now, we are presented with 2 options; one, guests can come to the house of the person on duty to retrieve keys, or can call that person to come bring the keys to them...or two, an unlocked keybox to hang the keys in for the guests to retrieve. That brings up the issue of security for the guests, as the keys would be left unattended for anyone to access. We have been going with option 1, but my wife was not too pleased when guests arrived last night and rang the doorbell at midnight and 1:30 am, respectively, and woke up our baby. 
I'm striving for the convenience of the keybox, with the added security of preventing public access to the keys. My plan for the enclosure is to build an enclosure similar to a standard lock-box, with a hole in the bottom and a small shelf-like tray beneath to catch the key...low enough to allow easy removal of that key, but not too low to allow someone to easily reach up into the enclosure to snag another key.
My initial thought on the key-holder switching mechanism would be a "trap-door" that holds the key through the keychain, maybe at a 100-degree angle, then drops to 0-degrees once the correct key code has been entered...allowing the key to slide off and into the tray below. I honestly think getting this aspect of the project to work correctly every single time, without creating too large of a box, is going to be my biggest challenge. The last thing I want out of this is to have a key get caught on another key/hook/wedged in the box, and the guest have to come find me anyway...but I don't want to create a monstrous box for 14 keys, either.
I REALLY appreciate the input thus far, and am quickly figuring out that I've got a lot of reading to do on the components used, as well as the programming to make it all happen. Thank you all a lot!