You should clarify your goals. For us and perhaps also for yourself.

Do you want to base the visuals on midi input or audio input. Midi input would require a midi library like midibus, promidi etc. Audio input would require a library like minim, sonia, beads etc. These are two very different routes and two very different codes. The midi route is probably the easiest, since you will already be getting a 'specific number' which can be fairly easily interpreted/mapped/etc.

Also, it's not yet relevant. But you don't say or show what the output should look like.

Trying is not a ridiculous goal. If you succeed, only time will tell. However a goal in itself can help fuel development and learning. And people always say you learn most from your mistakes. But try not to build a castle at once, do it brick-by-brick. Divide the problem into steps and try to tackly those one by one.

Hi --thank you so much for a kind response with very appreciated advice.

All right, this is much clearer and gives a better (and different) impression of your final project than the first post.

If you have existing sound samples, you can play them in Processing using Minim. For samples that you will be triggering a lot, check out the following example that comes with Processing: File > Examples > Libraries > Minim Audio > LoadSample

Drawing something by clicking and dragging the mouse is very easy. Check out the examples that come with Processing, for example under Topics > Drawing.

Colors and sounds can be stored in an array (which is like a basket holding a number of things). One could (instead) use classes and object-oriented programming, but that may be a bit to difficult for a beginner and is probably not required to realise the described project. However it is something to keep in mind for the future.

Getting midi into Processing is yet another seperate brick-in-the-castle. As mentioned there are several midi libraries available. However this is most likely the hardest aspect of your project. One more thing to keep in mind is, most people won't have your hardware, which makes specific questions harder to answer. So expect less help in that area.

Once these sub-parts are individually running, work towards combining them. If feasibility is your main concern, start with the biggest challenge, which is the midi connection. Otherwise start with the drawing-audio side as a mouse + keyboard driven project.

You mentioned you had existing sound samples. The signals are much less intuitive than the samples functionality in Minim actually. So my advice is to not 'waste time' on figuring those out, but to check out the examples closer to your intended project, such as:

File > Examples > Libraries > Minim Audio > LoadFile.

See the javadocs for the AudioPlayer class used in the mentioned example. As you can see it has all kinds of useful functionality like play, pause, rewind, isPlaying etc.

Which means it should enable you to play (pause, rewind) 1 or even 12 samples at will.