You won't be able to please everyone, I think you've figured that out by now.. Have you considered moving some inputs to the rear of the unit? A multi-purpose rotating knob would be more useful to me than front facing USB/SD/AUX inputs. These could all be moved to the back and let the user run cable wherever they want.
With a knob with click push, you can control a lot of things. Besides the usual volume up/down/mute, you could click hold to bring up a new set of menu options - Equalizer, Input settings, LCD control for example. Then use the knob as left/right or up/down and click select. Brings up your eq/lcd settings and so on, you get the idea. It's very intuitive vs trying to cram several single use buttons where they normally wouldn't make sense. This is the way BMW & Lexus (and prob others) are going - more features, less buttons.
I discuss these with the design guy. What he said is, there is really no room for the knob if we want to put a 7" LCD in this project. Even put them in one side, there is very tie plus that will not stable enough
for the SD slot, what ever a stand SD or mini SD, it won`t effect because it sitting there vertically. both take the same space