Can the sensitivity of the pad be changed?
Velocity can be changed in a DAW.
Is it possible with the board?
Yes, It is possible.
Can it work with the best DJ and plug in a Newmark Mixtrack Platinum?
Theoretically you would need a USB adapter for this,
I'm computer dumb ... is it working with the Ableton standard and a MacBook?
It will work with Ableton, not sure about the MacBook
How big is the drum pad?
Theoretically you would need a USB adapter for this, but you can use your mic on your PC.
If I bought used, will downloads still be included?
If the last owner did not use the download codes
I have Newmark Mixtrack Platinum, will it work properly?
I don’t think so. But you can try.