Multiple Speakers Feasibility and sound files

So my EGR class has been contacted by the local Natural History Museum to build exhibits for the new wing. Our exhibit my team has decided to build is a dinosaur foot print comparison platform. We are etching glass which will be lit by LEDs to give it that cool light effect. I have already written and tested the code for my 4 buttons to light the 4 different footprints we are making. My next step is to incorporate speakers so when the kids press the buttons the speaker will play that dinosaurs associated sound.roar file.

The bit of research i did shows i will need an SD card and the SD card to arduino converter. The sound files will need to be in .wav and there are some codes out there for if button a is pressed play sound file a. Will i need more than one Arduino UNO for this and what external power supplies should i consider… and as i am a second year engineering student we have not learned about playing audio files yet so this is new territory for me. When connecting speakers to power sources do they need any special resistors or can i connect them to my standard resistors in my circuit?

Thank you to anyone who takes time to answer any of my questions i do appreciate the help.

The Arduino by itself couldn't handle a .wav file. They can do some basic square wave tones, but not really produce good sound. It will require external hardware. There are some shields that will play wav files that can be connected to Arduino.

Here's an example but you might wait for someone with more experience with these shields than me to see if that's the best choice.

Will all 4 need to play at once? Then 4 separate players will be needed. Their outputs can be mixed and then fed into amplified speakers (desktop computer speakers for example).
You can send simple Serial.write(0x01) type commands to these modules to have them play a sound file.
Datarate needed is only 4800, some version of software serial would be fine.

CrossRoads:
Will all 4 need to play at once?

It is possible yes if a bunch of kids start getting on the exhibit and start mashing the buttons or one kid trying to press them all. We are going to have 4 separate speakers essentially only one speaker will play only one file over and over again.

Check here for amps & speakers on sale too
http://www.parts-express.com/
Maybe a few of these and some speaker cabinets:

Or a couple sets of these powered speaker sets

http://www.parts-express.com/spacetech-fx-8-powered-computer-speaker-pair--319-037