How should one practice pieces - both hands at a time or separately?
There is no unambiguous answer - supposedly the best approach is to learn bar after bar both hands at once; meaning that we read out one bar's worth of the right hand notes, then the same bar's left hand notes, then we connect them and learn to achieve perfection in playing it and then move on further. Some take a couple bars instead of one or even a whole page of notes. I use a different way - I learn a whole piece by hart at once in a stow time and then I practice to achieve perfection.
What kind of tuning do you use?
Standard (E, B, G, D, A, E), although I know it's a rarity with tappers. Stanley Jordan tunes E and B a semitone higher, thanks to that there is always a 4th between these strings. If you know whole sounds on the fingerboard by hart there is no need to change the tuning and make your playing difficult . Although Jordan's tuning has its advantages - it is meant to be much more logical, so on a double-necked guitar the higher neck is tuned to standard and the other one a 4th lower, in other words the lower neck has a set of strings with the wider diameter of a 7-string set (B, G, D, A, E, B).
Besides tapping, do you still play the traditional way?
Sometimes but rarely, certainly I'm not developing in regular approaches. I stopped playing the traditional way after our rock band had dissolved. The band used to play strong, melodious music.
Why double-necked guitar and not the Stick? Why two necks and not one but wider? What advantages does the second neck give you compared to a 6-string guitar?
Answer for these questions con be found in the Gear section.
How do you achieve a long sustain with each note, especially when playing longer on the same string?
The way the sound is created in such a technique is simple: nut and pickups. Finger hits the string making it vibrating. A big precision can be obtained using portato It allows (in my opinion) much more control over sound dynamics than regular legato.
Do you use distortion/compression playing tapping? No, I don't.