Is Arduino good for this application? (midi, audio, small scree)

Hi,
With Due, you don't need shield.
Look at my blog here : Groovuino: Groovuino groove box demo
In the end of video, you can see a pad which trigger the drums with velocity.
Audio is 44 kHz/12 bits, and samples are stored on an SD card.
You can make sampling, MIDI, synthesis, sequencing...