I don't do MLF as a matter of course but the only way I know to check
for completion is with paper chromatography or do what you are doing,
see when the tiny bubbles stop. You check to see if all the malic is
consumed.

> What do I do with
> the film on the top wine in the neck?

I can't think of a good film, so what I would do is overflow the carboy
to float it out. I use a wine thief with my finger over the vent and a
couple paper towels wrapped around the neck of the carboy to catch the
overflow. I would wipe out the neck and maybe add 20 PPM sulfite if a
film formed on any of mine . The sulfite will probably stop the mlf if
not complete though; maybe others who do mlf have a better plan to deal
with that.

Joe