I am afraid that I can only answer one of your questions: the others must be listed as separate postings. This answer will address what the poem theme.
The constant theme of the fleetingness of life is central to the poem. The daffodils the speaker and his lost "spouse" (we never know if the narrator is the husband or the wife) at one time used to cut and sell are symbolic of the speed with which life passes, as daffodils too last only a short time themselves, when cut.
The speaker talks about memories: those that remain and those forgotten by some. The abundance of the flowers might suggest that the daffodils became common place to the subject (he or she who died) of the poem and the speaker, until the flowers no longer seemed as spectacular as they once had, not only in terms of beauty, but also in terms of the importance they represented to their lives in making money. The person recalling the daffodils and their lives while harvesting the flowers (husband, wife and child) notes that the dead person's daughter does not remember the deceased parent or the picking of the flowers. This had not always been the case. At one time, they were perceived as a true blessing:
They simply came,
And they kept on coming.
As if not from the sod but falling from heaven.
The speaker notes that this was a time in their lives where they knew they would never die—but would learn much too soon that this is not the case.
We knew we'd live forever. We had not learned
What a fleeting glance of the everlasting
Daffodils are. Never identified
The nuptial flight of the rarest epherma-
Our own days!
We thought they were a windfall.
Never guessed they were a last blessing.
We get the sense from the speaker, also, the he/she feels that they were foolish to sell the flowers that seemed endless to them, as if the daffodils represented their days on earth together: that they did not pay close enough attention to their time together, taking it for granted as they did the flowers as well.
And we sold them.
It sounds like sacrilege, but we sold them.
Were we so poor?...We sold them, to wither.
The speaker describes the "wedding-present" scissors that they had used to cut the flowers, recalling also how they had lost them. The scissors may be symbolic of the loss of the marriage to death.
And as the poem comes to a close, the speaker refers to the scissors once again, that lie hidden somewhere, hidden by the daffodils, like a grave stone, marking the place where they once worked together.
But somewhere your scissors remember. Wherever they are.
Here somewhere, blades wide open,
April by April
Through the sod—an anchor, a cross of rust.
The scissors "remember," as the speaker assures us, he does also.