I'll answer each of your questions in order:
The notes in parentheses are ghost notes. You should play them quietly - certainly don't emphasize them. They do have rhythmic value, however (i.e. they aren't grace notes).
The 7 to 9 slide is a legato slide. Pick the 7, then slide to 9, but don't pick again for the 9.
The 5-7-5, 7-5-0 are indeed hammer-ons and pull-offs. The same legato notation works for both: if a note is followed by a higher note, it will be a hammer-on; if it is followed by a lower note, it will be a pull-off. So in your example, 5-7-5 is a hammer-on (5-7) followed by a pull-off (7-5). The 7-5-0 would be two pull-offs (7-5, 5-0).
I'm not entirely sure about the next one (in this case it might help to see the staff notation). Certainly you would play the chord and then play the hammer-ons and pull-offs on the top line (B string). Possibly you should keep the rest of the chord fretted so it will ring, or at least the 6 on the G string for a gentle pull-off to (0) at the end. But I'm not certain.
The 14-12-14-12 etc with the long line over-top is a long series of pull-offs and hammer-ons.
The 15 to 17 slide with the legato marking has the same meaning as the 7 to 9 slide in your first question: pick 15, slide to 17, don't pick again. The 17 to 10 slide means pick the 17, slide to 19, and pick again.