#2
It means it uses the 1st 4th and 5th degrees of the respective scale in this case A

1-b3-5 for example is a minor chord 1-3-5 is a major chord that kinda thing
#3
So does this tell me what kind of chords I could go to. For instance:

A sus4 - Em - F

Would that work?
#4
Steps are used for telling which degrees of a scale are in a chord, not which chords to play. A chord progression using roman numerals says which chords to play.

Ex: Given I-IV-V-ii-I in key of C would be:
C-F-G-dm-C.
breaking hearts
&
breaking guitars