@Bill G This looks great! My only suggestion right now is to move the "Me.SetFocus" out of AutoComplete_Container.AC_Listbox.MouseEnter and have it in the AC_Listbox.MouseMove instead.
Every time I've tested this, I've clicked in the textbox to get the cursor and then without meaning to, let the mouse move down a bit into the open area below. Then when I start typing, it sees the mouse was there and sets the focus to the listbox and highlights an entry, making it impossible for me to type any more. Moving the SetFocus into the MouseMove fixes that for me.
Anyway, great work, thanks!
Done! Thanks again Bill!