What effect would converting the lowest denomination note to a coin be?
The usual rationale for replacing notes with coins is that small-denomination notes and coins circulate heavily, and notes need to be replaced much more often than coins. However, as an example, the costs of transitioning to a dollar coin (think vending machines, etc.) in the U.S. would be significant enough to make the change not worthwhile, according to a FRB staff working paper. See "Costs and Benefits of Replacing the \$1 Federal Reserve Note with a $1 U.S. Coin" for details on their approach, which covers the issues pretty well.