Why does the Torah insert the (otherwise superfluous) word "Echad Achuz min ha'Chamishim"
Yerushalmi T'rumos, 4:2: To teach us that 'Whatever one removes from one location should be one fiftieth' - with reference to the medium Shi'ur of Terumah. 1
See Torah Temimah, note 36.
Why does the Torah insert with regard to the Levi'im here and in 47 "Shomrei Mishmeres Mishkan Hashem"?
Oznayim la'Torah #1: To stress that the tax was not in order to repay the Levi'im for having redeemed Yisrael and their animals fom the B'chorah, 1 but because they guarded in the Mishkan.
Oznayim la'Torah #2: To stress that, although they were about to enter Eretz Yisrael and would no longer be required to carry the Mishkan, they would retain their elevated status still they would still do guard duty in the Beis Hamikdash.
Oznayhim la'Torah: See Bamidbar, 3:45.
