w/salaam,
Re: 1)
Establish the salat at the setting of the sun to the darkness of the night; and the reading (of) dawn; indeed, the reading (of) dawn is witnessed. [17:78]
And from the night so remain awake
with it additionally for yourself, perhaps your Lord will raise you (to) a status praiseworthy. [17:79]
The "
with it" (Arabic: bi hi) refers to a preceding masculine noun, and thus can ONLY refer to "reading" (Arabic: quran). Note that "salat" is a feminine noun. Thus, the idea of "the tahajjud prayer" is not possible unless one considers it as a reading (also see 73:20).
Reading/quran is self explanatory is it not?
Re: 2)
Have you considered looking up the meanings/occurrences of those words using:
http://corpus.quran.com/http://www.studyquran.co.uk/PRLonline.htmRe: 3)
no
See 5:6, 4:43