Why does it mention taking donkeys and Tzon, but not cattle?
Radak: Cattle is not mentioned in the Parshah; it is included in "Tzon". 1
Even though normally, Tzon is only sheep and goats. (PF)
Why does it say "for his servants" regarding Ma'aser of Peros, but not regarding Ma'aser of animals?
Malbim: Peros are not so important to him; he gives them to his servants. He will take Ma'aser of your animals for himself, to get rich.
What does "you will be to him slaves" add? It already says that he may take your children, land, produce, slaves and animals!
Radak: He may impose taxes on you. It says here "la'Avadim", like "Yihyu Lecha la'Mas va'Avaducha" (Devarim 20:11).