2) The common opinion is that it's a rainy day fund. The church has a lot of expenses, including lots of real estate and fancy buildings worldwide. If there was a drop in tithing or a major economic recession, they want to be able to weather it for an indefinite period.
4) Nothing major has been done. Last year, there was a church policy update that states
> ...using friendship or a position of trust to take financial advantage of another is “a shameful betrayal of trust and confidence. Its perpetrators may be subject to criminal prosecution. Church members who commit affinity fraud may also face membership restrictions or withdrawal. … Members may not state or imply that their business dealings are sponsored by, endorsed by, or represent the Church or its leaders.”
(https://www.thechurchnews.com/2021/3/31/23216752/updates-gen...)
But that's the whole of it. No recent major sermons call out MLMs and their ilk.