Here's what I usually do.
1)Standard sized TV/movie cels get a new bag. All
layers are also bagged separately. Small to
medium pan cels usually stay in the same bag
since I don't have any bags to fit them. If the
bag is in bad shape I tape a few new smaller bags
together to fit. Large cels (too big to fit in
largest Itoya) get professionally framed (I don't
trust my own framing skills)
2)I remove all staples and tape very carefully.
3)Depends. If the layers are not stuck I gently
clean with either water or small amount of
rubbing alcohol(to be quickly washed off
afterwards). If the layers are stuck, I don't try
to force them apart nor try to clean them since
I'm worried about damaging them and getting
cleaning agents trapped between layers.
4)I scan out of the bag. The only exceptions have
been a few cels that came to me already framed. I
just scanned them through the glass and hoped for
5)I keep the sketches separate from the cels
since they take up too much room in the
portfolios. All sketches from the same cel
(anywhere from 1 to 30) share the same bag. I
keep the backgrounds with the cels. Since the
portfolios are supposed to be acid-free and the
backgrounds shouldn't stick to anything, they are
not bagged separately like the cel layers.
6)Like everyone else so far, I really hate stuck
sketches. If they are only lightly stuck I just
work at them very slowly until they come apart. I
have been tempted by the freezer method, but
haven't tried it yet. I had a few that were VERY
stuck and paid a restoration company to separate
them. I have mixed feelings about the results and
feel its probably not worth the cost unless the
cel is very valuable.