Now, the ideal is for the church to support those ministries. NT church is not a storehouse, has a world evangelism focus temple didn't have. It's more a clearing house than a storehouse. Lots of phony and unworthy parachurch ministries today. Church elders in a better position to evaluate than average person.
Freewill offerings can go anywhere.
I don't think there's any other passage quite like this one. Like God longs for us to give him a chance. You can't outgive God. God doesn't call on us to start robbing him less, but to stop robbing him at all. Moses commands the people to stop giving.