The Levites were to give a tithe of the tithe they received from the people to the priests. This tithe was to include the best of what the other Israelites gave to them ( Numbers 18:30; Numbers 18:32). [source][source][source]
"Whereas in heathen states, where there was an hereditary priestly caste, that caste was generally a rich one, and held a firm possession in the soil (in Egypt, for example; see at Gen. xlvii22), the Levites received no hereditary landed property in the land of Israel, but only towns to dwell in among the other tribes, with pasturage for their cattle (chap. xxxv.), because Jehovah, the God of Israel, would be their inheritance." [1][source]
Had the Israelites been faithful in their tithing the Levites would have received about five times as much as ordinary Israelites (cf. Genesis 43:34). Unfortunately the Jews were not completely obedient to these laws. [source][source][source]
"What is to be made of the writer"s exclusion of Moses in these matters that relate so closely to the duties of the priests? Why is Moses so conspicuously left out of the picture [2]? The answer perhaps lies in the author"s desire to tell us something about the role of Moses as leader of God"s people. His role is not limited to the work of a priest. Aaron is shown here assuming most of that responsibility. In the view of the writer, then, it appears that the role of Moses was becoming more distinct from the office of priest. Thus the writer attempts to show that Moses" role as mediator of the covenant, already well established throughout these narratives, was not merely a priestly one. There is a concern to show that he also functioned in the role of prophet as well as king, two themes that will receive further development in the book of Deuteronomy ( Deuteronomy 18:15; Deuteronomy 33:5). Hence as the picture of Moses develops within the Pentateuch, it more closely resembles the future messianic ruler, who is anticipated already in the Pentateuch as a prophet, a priest, and a king." [3][source]