Best Arduino for Midi-Board
If you have not done product design many times before, you will learn it is not that easy to do as good a job as they did .

One reviewer said "The Loupedeck’s build quality is very good; nothing feels loose or cheap." 


You might be able to improve it starting with the unit , but it does not look poorly designed on the outside. But may need care from abuse. 

Maybe you really want this.


I realize everything that was asked, but sometimes people have no clue what it takes for the expected high class design requested. It is not trivial even for EE grad's with 10 yrs experience. It comes from working on the job with the best experts. 

The best answer comes from decades of practical experience. But if you have none, this is over-ambitious for a 1st time.  Start with a plan. Digital is always bettern than analog because of the reliability aspect and incremental digital volume controls are exclusively used now, instead of pots in high quality equipment ( cars , DSO's etc.) The question indicates no experience which even the best in this forum would have a hard time doing everything , electrical, mechanical,  polymer overlay, EMI, tactile feel, an ergonomic 1st class  HMI etc required and make it "better" than this example.  If you know nothing about integration design , EMI and ESD proof, you have a long road to haul without mentors on the job.  

Frankly it's hard to do it better. But if you want to learn start with an Arduino and their Mickey Mouse Shields or an RPi and shop for digital peripherals and learn to integrate 100 analog and/or digital I/O's in real time. 

But start with a good "spec" and a better plan. Have fun.