When did they see that there is much money in the Aron?
Rashi: Every day (constantly). Radak - they would empty it out and return it to its place, like it says in Divrei ha'Yamim II, 24:11.
Malbim (here and in Divrei ha'Yamim II, 24:11): This was from new hsTerumas ha'Lishkah. Three times a year they took Shekalim to buy Temidim and Musafim; the remainder was for Bedek ha'Bayis.
Here it says that Sofer ha'Melech and the Kohen Gadol counted the money. In Divrei ha'Yamim II, 24:11 it says that Sofer ha'Melech and the Kohen Gadol's appointee counted it!
'Rashi' (Divrei ha'Yamim II, 24:11): Also here, it means that the Kohen Gadol sent his Shali'ach (the Segan) to count. It is not honorable for the Kohen Gadol to go with the king's servant.
Why does it say "va'Yatzuru"?
Radak: After counting the money, they wrapped it.
