1)
What are the ramifications of "me'Eis ha'Rav Tarbu u'me'Eis ha'Me'at Tam'itu"?
1.
Ramban (citing Bava Basra 122a): It refers, not to the tribes, who each gave an equal number of towns, 1 but to the families, 2 who gave according to their size.
2.
Targum Yonason and Seforno: The larger tribes gave more towns (though the value of the towns that each tribe gave was the same - Seforno) 3 :
2)
Why does the Torah add the (otherwise superfluous) words "Yitein me'Arav la'Levi'im"?
1.
Rashi (in Yehoshua. 21:5): To teach us that each tribe had to provide towns for the Levi'im.