Angels are mentioned many times in both the Old and New Testaments (296 times according to my computer search). They are an important way that God achieves his purposes.
The reason why it is believed that each person has guardian angels is:
Matthew 18:10 “See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven.
And Jesus certainly had angels to guard him.
Luke 4:10 for it is written, “‘He will command his angels concerning you, to guard you,’
There is no Biblical evidence that I am aware of that humans ever become angels. The origin of angels is not discussed anywhere in scripture. However their role (or at least one of their roles) is described as helping those who will inherit salvation:
Hebrews 1:13-14 And to which of the angels has he ever said, “Sit at my right hand until I make your enemies a footstool for your feet”? (14) Are they not all ministering spirits sent out to serve for the sake of those who are to inherit salvation?
There is some evidence that angels are not promoted people, because:
1 Corinthians 6:3 Do you not know that we are to judge angels? How much more, then, matters pertaining to this life!
“Judging” implies that the angel being “judged” is in an inferior position to the one doing the judging. This means that it is unlikely that the angel is a glorified person.
The gloried saints are describes as being like the angels, which would be a surprising thing to say if gloried saints will be angels.
Matthew 22:30 For in the resurrection they neither marry nor are given in marriage, but are like angels in heaven.
So yes, angels are important. But no, there is no reason to believe that we can become angels.