Gold star! A great ELI5.

I would just add one detail: the "healthy" inflation you refer to is the government printing a small amount of money, not the natural growth of the economy, since currency is fungible and affects the relative price of everything without bias. All other effects on inflation are really localized destabilization of market forces, which have a biased effect on the market and cause problems.

If the government prints too much money, that's dangerous in a different way: money "moves" too fast for people to react. So a moderate amount of inflation like 1% is comfortable for an ordinary person to deal with, but the larger that inflation, the more difficult it is for people to react, because, well financial activity, like renegotiating a salary or changing the prices of apples or buying investments, moves at a fixed pace.

If money inflates, then everything else deflates relative to it (meaning people will want to hold anything else more than money relative to that money). The one caveat here is that there are different currencies inflating (due to money printing) at different rates (in addition to other market effects).