Rav Shimshon Raphael Hirsch writes in Chorev here (second paragraph) that after we have encircled the Bimah seven times we beat the Aravos as a means to remove any sense of Ga'avah (haughtiness / arrogance) from our hearts and the belief that our successes come from us alone. He says that the Aravah is symbolic of the 'chomer' lit. the material i.e. it is ...
Ritva (c. 1300 Spain) changes the girsa: the defining feature is not fruit tasting like wood, but rather the branches cover the wood.
Rashash (19th century Lithuania): Read the word "anaf" as "anav", interchanging the pey with the beis, indicating that Hadas is the branch "anaf" which resembles the fruit "anav".
Yes. There is a nice idea which is to use the object used for a mitzva for another one, e.g., I have seen
some use the etrog for besamim (spices) during havdala, by planting cloves into the etrog
people often burn the four species before Pesach together with the hamets
Beyond this you can also
make etrog jam
use the hadasim for a bouquet
see here at ...