>1) Is there a way to DRAW using SCREEN 0?
I don't think so.
2) How do you clear the previously pressed keys?
I don't use QB64, but in qbasic:
do while len(inkey$): loop
would do it.
This _KEYHIT of which you speak: does it not remove the keystrokes from the buffer as it reads them? If not, why don't you use a function that does?