kimouette wrote: Could you tell me how much the LCD screen would cost?
about 8 to 12 euros.
kimouette wrote: About the external power supply...
Is that part of the board made for a battery power supply (a 9 volt battery?) or for an external alim power (wall) supply?
For an external alim power (wall) supply.
kimouette wrote:About the inputs that are related to the hi hat...
#3 - Power source for HiHat controller
#4 - HiHat controller input
#7 - HiHat Bow
#8 - HiHat Edge
Inputs 7 and 8 seem clear : I just have to plug the piezo's wires into this input. But are the inputs 3 and 4 also ONE SINGLE stereo input?
Yes.
kimouette wrote: And would that input be the one used to plug the potentiometer/variable controller (like the one created by Beatnik)? Or is #4 for the potentiometer and #3 another input that needs to be linked to something else?
#3 and #4 are used to plug the potentiometer/variable controller.
kimouette wrote: What's with the input #6?
Not connected.
kimouette wrote: Is that where the 4 pushbuttons will be connected? And what kind of menus do we get? options like Velocity control? effects? or something else?
http://www.megadrum.info/forums/viewtopic.php?f=3&t=187&p=3481#p3481
http://www.megadrum.info/menu_layout.pdf
kimouette wrote:About the power switch...
Is is better (I mean safer) to have one? Or does simply plugging the megadrum ( with either the USB cable or the external power supply) works fine?
As you wish.
kimouette wrote:About the led...
What's the use of the led?
Is it also included in the "All in one + components" kit?
The LED is used for MIDI activity.
Yes, it's also included in the "All in one + components" kit.