Answer:
I am lighter than air but a hundred people cannot lift me. Careful! I am fragile!
I am a busy worker who is a water mammal.
Born of sorrow, grows with age, you need a lot to be a sage. What is it?
Glittering points that downward thrust. Sparkling spears that never rust.
I fill a room but take no space.
It is something you make after you've weighed your options.