1)
What money did they collect?
1.
Malbim: Here it explains that the Leviyim collected from Yisrael. In Melachim II, Perek 12, regarding Yo'ash it explains that there were two monies ? that brought to Beis Hashem, and what the Leviyim collected from Yisrael. Melachim II, 22:4 includes both together, concisely.
2)
What are "Shomerei ha'Saf"?
1.
Radak (Melachim II, 22:5): They guard the Kelim of the Beis ha'Mikdash.
2.
Radak (Melachim II, 22:5, citing Targum Yonasan): They are Gizbarim (overseers of Hekdesh).
